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, 14 insertions, 0 deletions

diff --git a/src/rio.c b/src/rio.c
index f99913152..bcda3767b 100644
--- a/src/rio.c
+++ b/src/rio.c
@@ -438,6 +438,20 @@ void rioSetAutoSync(rio *r, off_t bytes) {
     r->io.file.autosync = bytes;
 }
 
+/* Check the type of rio. */
+uint8_t rioCheckType(rio *r) {
+    if (r->read == rioFileRead) {
+        return RIO_TYPE_FILE;
+    } else if (r->read == rioBufferRead) {
+        return RIO_TYPE_BUFFER;
+    } else if (r->read == rioConnRead) {
+        return RIO_TYPE_CONN;
+    } else {
+        /* r->read == rioFdRead */
+        return RIO_TYPE_FD;
+    }
+}
+
 /* --------------------------- Higher level interface --------------------------
  *
  * The following higher level functions use lower level rio.c functions to help