tipc: Fix race condition when creating socket or native port

This patch eliminates the (very remote) chance of a crash resulting
from a partially initialized socket or native port unexpectedly
receiving a message.  Now, during the creation of a socket or native
port, the underlying generic port's lock is not released until all
initialization required to handle incoming messages has been done.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>