core: firewall integration with DynamicUserNFTSet=

New directive `DynamicUserNFTSet=` provides a method for integrating
configuration of dynamic users into firewall rules with NFT sets.

Example:
```
table inet filter {
        set u {
                typeof meta skuid
        }

        chain service_output {
                meta skuid != @u drop
                accept
        }
}
```

```
/etc/systemd/system/dunft.service
[Service]
DynamicUser=yes
DynamicUserNFTSet=inet:filter:u
ExecStart=/bin/sleep 1000

[Install]
WantedBy=multi-user.target
```

```
$ sudo nft list set inet filter u
table inet filter {
        set u {
                typeof meta skuid
                elements = { 64864 }
        }
}
$ ps -n --format user,group,pid,command -p `pgrep sleep`
    USER    GROUP     PID COMMAND
   64864    64864   55158 /bin/sleep 1000
```

1 files changed, 24 insertions, 0 deletions

diff --git a/man/org.freedesktop.systemd1.xml b/man/org.freedesktop.systemd1.xml
index 6625a74073..b9b5768bf0 100644
--- a/man/org.freedesktop.systemd1.xml
+++ b/man/org.freedesktop.systemd1.xml
@@ -2785,6 +2785,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly b DynamicUser = ...;
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
+      readonly a(iss) DynamicUserNFTSet = [...];
+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly b RemoveIPC = ...;
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly a(say) SetCredential = [...];
@@ -3332,6 +3334,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {
 
     <!--property DynamicUser is not documented!-->
 
+    <!--property DynamicUserNFTSet is not documented!-->
+
     <!--property RemoveIPC is not documented!-->
 
     <!--property SetCredential is not documented!-->
@@ -3940,6 +3944,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2eservice {
 
     <variablelist class="dbus-property" generated="True" extra-ref="DynamicUser"/>
 
+    <variablelist class="dbus-property" generated="True" extra-ref="DynamicUserNFTSet"/>
+
     <variablelist class="dbus-property" generated="True" extra-ref="RemoveIPC"/>
 
     <variablelist class="dbus-property" generated="True" extra-ref="SetCredential"/>
@@ -4679,6 +4685,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2esocket {
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly b DynamicUser = ...;
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
+      readonly a(iss) DynamicUserNFTSet = [...];
+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly b RemoveIPC = ...;
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly a(say) SetCredential = [...];
@@ -5250,6 +5258,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2esocket {
 
     <!--property DynamicUser is not documented!-->
 
+    <!--property DynamicUserNFTSet is not documented!-->
+
     <!--property RemoveIPC is not documented!-->
 
     <!--property SetCredential is not documented!-->
@@ -5852,6 +5862,8 @@ node /org/freedesktop/systemd1/unit/avahi_2ddaemon_2esocket {
 
     <variablelist class="dbus-property" generated="True" extra-ref="DynamicUser"/>
 
+    <variablelist class="dbus-property" generated="True" extra-ref="DynamicUserNFTSet"/>
+
     <variablelist class="dbus-property" generated="True" extra-ref="RemoveIPC"/>
 
     <variablelist class="dbus-property" generated="True" extra-ref="SetCredential"/>
@@ -6480,6 +6492,8 @@ node /org/freedesktop/systemd1/unit/home_2emount {
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly b DynamicUser = ...;
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
+      readonly a(iss) DynamicUserNFTSet = [...];
+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly b RemoveIPC = ...;
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly a(say) SetCredential = [...];
@@ -6979,6 +6993,8 @@ node /org/freedesktop/systemd1/unit/home_2emount {
 
     <!--property DynamicUser is not documented!-->
 
+    <!--property DynamicUserNFTSet is not documented!-->
+
     <!--property RemoveIPC is not documented!-->
 
     <!--property SetCredential is not documented!-->
@@ -7499,6 +7515,8 @@ node /org/freedesktop/systemd1/unit/home_2emount {
 
     <variablelist class="dbus-property" generated="True" extra-ref="DynamicUser"/>
 
+    <variablelist class="dbus-property" generated="True" extra-ref="DynamicUserNFTSet"/>
+
     <variablelist class="dbus-property" generated="True" extra-ref="RemoveIPC"/>
 
     <variablelist class="dbus-property" generated="True" extra-ref="SetCredential"/>
@@ -8254,6 +8272,8 @@ node /org/freedesktop/systemd1/unit/dev_2dsda3_2eswap {
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly b DynamicUser = ...;
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
+      readonly a(iss) DynamicUserNFTSet = [...];
+      @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly b RemoveIPC = ...;
       @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
       readonly a(say) SetCredential = [...];
@@ -8739,6 +8759,8 @@ node /org/freedesktop/systemd1/unit/dev_2dsda3_2eswap {
 
     <!--property DynamicUser is not documented!-->
 
+    <!--property DynamicUserNFTSet is not documented!-->
+
     <!--property RemoveIPC is not documented!-->
 
     <!--property SetCredential is not documented!-->
@@ -9245,6 +9267,8 @@ node /org/freedesktop/systemd1/unit/dev_2dsda3_2eswap {
 
     <variablelist class="dbus-property" generated="True" extra-ref="DynamicUser"/>
 
+    <variablelist class="dbus-property" generated="True" extra-ref="DynamicUserNFTSet"/>
+
     <variablelist class="dbus-property" generated="True" extra-ref="RemoveIPC"/>
 
     <variablelist class="dbus-property" generated="True" extra-ref="SetCredential"/>