[SOCK][NETNS]: Add the percpu prot_inuse counter in the struct net.

Such an accounting would cost us two more dereferences to get the
percpu variable from the struct net, so I make sock_prot_inuse_get
and _add calls work differently depending on CONFIG_NET_NS - without
it old optimized routines are used.

The per-cpu counter for init_net is prepared in core_initcall, so
that even af_inet, that starts as fs_initcall, will already have the
init_net prepared.

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

include/net/netns/core.h

@@ -2,12 +2,15 @@
 #define __NETNS_CORE_H__
 
 struct ctl_table_header;
+struct prot_inuse;
 
 struct netns_core {
 	/* core sysctls */
 	struct ctl_table_header	*sysctl_hdr;
 
 	int	sysctl_somaxconn;
+
+	struct prot_inuse	*inuse;
 };
 
 #endif