ctdb-protocol: Initialise request->rdata.opcode where missing

ctdb-protocol: Initialise request->rdata.opcode where missing

Otherwise it is uninitialised, so...

==22889== Conditional jump or move depends on uninitialised value(s)
==22889==    at 0x12257B: ctdb_req_control_data_len (protocol_control.c:39)
==22889==    by 0x1228E9: ctdb_req_control_len (protocol_control.c:1786)
==22889==    by 0x12A51C: ctdb_client_control_send (client_control.c:101)
==22889==    by 0x138BE1: ctdb_tunnel_setup_send (client_tunnel.c:100)
==22889==    by 0x10EE4F: tunnel_test_send (tunnel_test.c:135)
==22889==    by 0x10EE4F: main (tunnel_test.c:463)

and similar.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>