netfilter: assign PDE->fops before gluing PDE into /proc tree

Replace create_proc_entry with specially created for this purpose proc_create.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>