[NETNS]: Make icmp_sk per namespace.

All preparations are done. Now just add a hook to perform an
initialization on namespace startup and replace icmp_sk macro with
proper inline call.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netns/ipv4.h

@@ -26,6 +26,8 @@ struct netns_ipv4 {
 	struct hlist_head	*fib_table_hash;
 	struct sock		*fibnl;
 
+	struct sock		**icmp_sk;
+
 	struct netns_frags	frags;
 #ifdef CONFIG_NETFILTER
 	struct xt_table		*iptable_filter;