dhcp: use the attached sd_device object when generating IAID

Note, previously `use_mac` set with `test_mode`. As `dev`, which is set with
`client->dev`, is not set when running test or fuzzer. Hence, the condition
```
if (udev_available() && !use_mac)
```
is effectively equivalent to
```
if (dev)
```
So, this commit mostly does not change behavior. Except for the following
corner case.

The sd_device object assigned from networkd (that is, Link.dev) never
has ID_RENAMING udev property, as sd_device objects which has the property
are filtered out at `link_check_initialized()` or `manager_udev_process_link()`
in networkd-link.c.

However, sd_device object created in `dhcp_identifier_set_iaid()` in the
previous code may have it. Such situation may (at least, theoretically)
happen when the network interface is renamed after initialized, e.g. by
creating the following spurious .link file:
```
[Match]
OriginalName=eno1
[Link]
Name=lan
```
and then trigger uevent for the network interface while systemd-networkd
calling `dhcp_identifier_set_iaid()`.

1 files changed, 3 insertions, 5 deletions

diff --git a/src/libsystemd-network/test-dhcp-client.c b/src/libsystemd-network/test-dhcp-client.c
index 8344dc4f4a..0f3a68e990 100644
--- a/src/libsystemd-network/test-dhcp-client.c
+++ b/src/libsystemd-network/test-dhcp-client.c
@@ -144,10 +144,8 @@ static void test_dhcp_identifier_set_iaid(void) {
         uint32_t iaid_legacy;
         be32_t iaid;
 
-        assert_se(dhcp_identifier_set_iaid(42, &hw_addr, /* legacy = */ true,
-                                           /* use_mac = */ true, &iaid_legacy) >= 0);
-        assert_se(dhcp_identifier_set_iaid(42, &hw_addr, /* legacy = */ false,
-                                           /* use_mac = */ true, &iaid) >= 0);
+        assert_se(dhcp_identifier_set_iaid(NULL, &hw_addr, /* legacy = */ true, &iaid_legacy) >= 0);
+        assert_se(dhcp_identifier_set_iaid(NULL, &hw_addr, /* legacy = */ false, &iaid) >= 0);
 
         /* we expect, that the MAC address was hashed. The legacy value is in native
          * endianness. */
@@ -169,7 +167,7 @@ static int check_options(uint8_t code, uint8_t len, const void *option, void *us
                 size_t duid_len;
 
                 assert_se(dhcp_identifier_set_duid_en(/* test_mode = */ true, &duid, &duid_len) >= 0);
-                assert_se(dhcp_identifier_set_iaid(42, &hw_addr, /* legacy = */ true, /* use_mac = */ true, &iaid) >= 0);
+                assert_se(dhcp_identifier_set_iaid(NULL, &hw_addr, /* legacy = */ true, &iaid) >= 0);
 
                 assert_se(len == sizeof(uint8_t) + sizeof(uint32_t) + duid_len);
                 assert_se(len == 19);