Phonet: listening socket lock protects the connected socket list

The accept()'d socket need to be unhashed while the (listen()'ing)
socket lock is held. This fixes a race condition that could lead to an
OOPS.

Signed-off-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>