Adds isolated netstats for replication. (#10062)

The amount of `server.stat_net_output_bytes/server.stat_net_input_bytes`
is actually the sum of replication flow and users' data flow. 
It may cause confusions like this:
"Why does my server get such a large output_bytes while I am doing nothing? ". 

After discussions and revisions, now here is the change about what this
PR brings (final version before merge):
- 2 server variables to count the network bytes during replication,
     including fullsync and propagate bytes.
     - `server.stat_net_repl_output_bytes`/`server.stat_net_repl_input_bytes`
- 3 info fields to print the input and output of repl bytes and instantaneous
     value of total repl bytes.
     - `total_net_repl_input_bytes` / `total_net_repl_output_bytes`
     - `instantaneous_repl_total_kbps`
- 1 new API `rioCheckType()` to check the type of rio. So we can use this
     to distinguish between diskless and diskbased replication
- 2 new counting items to keep network statistics consistent between master
     and slave
    - rdb portion during diskless replica. in `rdbLoadProgressCallback()`
    - first line of the full sync payload. in `readSyncBulkPayload()`

Co-authored-by: Oran Agra <oran@redislabs.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/rdb.c b/src/rdb.c
index 62ec5bbb2..1faecd2f3 100644
--- a/src/rdb.c
+++ b/src/rdb.c
@@ -2782,6 +2782,9 @@ void rdbLoadProgressCallback(rio *r, const void *buf, size_t len) {
         processEventsWhileBlocked();
         processModuleLoadingProgressEvent(0);
     }
+    if (server.repl_state == REPL_STATE_TRANSFER && rioCheckType(r) == RIO_TYPE_CONN) {
+        atomicIncr(server.stat_net_repl_input_bytes, len);
+    }
 }
 
 /* Save the given functions_ctx to the rdb.