[SOCK]: Drop per-proto inuse init and fre functions (v2).

Constructive part of the set is finished here. We have to remove the
pcounter, so start with its init and free functions.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>