Fix NULL pointer dereference in tcp_nuke_addr.

tcp_nuke addr only grabs the bottom half socket lock, but not the
userspace socket lock. This allows a userspace program to call
close() while the socket is running, which causes a NULL pointer
dereference in inet_put_port.

Bug: 23663111
Bug: 24072792
Change-Id: Iecb63af68c2db4764c74785153d1c9054f76b94f
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>