Merge #20214: test: Fix rpc_net intermittent issue

fa5f466 test: Fix rpc_net intermittent issue (MarcoFalke)

Pull request description:

  Without the sync, the nodes might generate blocks at the same height and thus never be able to sync

ACKs for top commit:
  practicalswift:
    ACK fa5f466: patch looks correct

Tree-SHA512: 21255795c2121c71fc620beb766855e57c7af94a668331d1b625665e22eb4b485a2b5c3ad2bb9a7042744f3c3e49c71251bcec41ba25bca03fd54aae32968a3a

Author: fanquake

test/functional/rpc_net.py

@@ -54,6 +54,7 @@ def run_test(self):
         # Connect nodes both ways.
         self.connect_nodes(0, 1)
         self.connect_nodes(1, 0)
+        self.sync_all()
 
         self.test_connection_count()
         self.test_getpeerinfo()