tipc: Fix race condition that could cause accept() to fail

This patch ensurs that accept() returns successfully even when
the newly created socket is immediately disconnected by its peer.
Previously, accept() would fail if it was unable to pass back
the optional address info for the socket's peer before the
socket became disconnected; TIPC now allows accept() to gather
peer address information after disconnection.  As a bonus, the
revised code accesses the socket's port more efficiently, without
the overhead incurred by a reference table lookup.

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