[IrDA]: af_irda.c cleanups

We lock the socket when both releasing and getting a disconnected
notification. In the latter case, we also ste the socket as orphan.
This fixes a potential kernel bug that can be triggered when we get the
disconnection notification before closing the socket.

Signed-off-by: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>