[TCP]: Consolidate checking for tcp orphan count being too big.

tcp_out_of_resources() and tcp_close() perform the
same checking of number of orphan sockets. Move this
code into common place.

Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>