[IPV6] MROUTE: Add stats in multicast routing module method ip6_mr_forward().

This patches adds a call to increment IPSTATS_MIB_OUTFORWDATAGRAMS
when forwarding the packet in ip6_mr_forward() in the IPv6 multicast
routing module (net/ipv6/ip6mr.c).
Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6mr.c

@@ -1354,7 +1354,7 @@ int ip6mr_ioctl(struct sock *sk, int cmd, void __user *arg)
 
 static inline int ip6mr_forward2_finish(struct sk_buff *skb)
 {
-	/* XXX stats */
+	IP6_INC_STATS_BH(ip6_dst_idev(skb->dst), IPSTATS_MIB_OUTFORWDATAGRAMS);
 	return dst_output(skb);
 }