migration/multifd: sync packet_num after all thread are done

migration/multifd: sync packet_num after all thread are done

Notification from recv thread is not ordered, which means we may be
notified by one MultiFDRecvParams but adjust packet_num for another.

Move the adjustment after we are sure each recv thread are sync-ed.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20190604023540.26532-1-richardw.yang@linux.intel.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>