test: enable v2 transport for rpc_net.py

- "transport_protocol_type" of inbound peer before version handshake
  is "detecting" on p2p v2 nodes (as opposed to "v1" for p2p v1)
- size of a ping/pong message is 29 bytes (as opposed to 32 for p2p v1)
- for the sendmsgtopeer RPC sub-test, enforce p2p v1 connection to
  have a peer id of zero

test/functional/test_runner.py

@@ -240,6 +240,7 @@ BASE_SCRIPTS = [
     'p2p_getdata.py',
     'p2p_addrfetch.py',
     'rpc_net.py',
+    'rpc_net.py --v2transport',
     'wallet_keypool.py --legacy-wallet',
     'wallet_keypool.py --descriptors',
     'wallet_descriptor.py --descriptors',