ctdb-daemon: Check packet generation against database generation

ctdb-daemon: Check packet generation against database generation

CTDB verifies the generation in the packet header matches that of the
current generation.  However, that check now needs to be done where
database context is available.  So add in the check in handlers for
database requests (CTDB_REQ_CALL, CTDB_REQ_DMASTER, CTDB_REPLY_DMASTER
and CTDB_REPLY_CALL).

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