IPVS: fix NULL ptr dereference in ip_vs_ctl.c ip_vs_genl_dump_daemons()

ipvsadm -ln --daemon will trigger a Null pointer exception because
ip_vs_genl_dump_daemons() uses skb_net() instead of skb_sknet().

To prevent others from NULL ptr a check is made in ip_vs.h skb_net().

Signed-off-by: Hans Schillstrom <hans.schillstrom@ericsson.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index 33733c8..ae47090 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -3120,7 +3120,7 @@
 static int ip_vs_genl_dump_daemons(struct sk_buff *skb,
 				   struct netlink_callback *cb)
 {
-	struct net *net = skb_net(skb);
+	struct net *net = skb_sknet(skb);
 	struct netns_ipvs *ipvs = net_ipvs(net);
 
 	mutex_lock(&__ip_vs_mutex);