snmp: Remove duplicate OUTMCAST stat increment

the OUTMCAST stat is double incremented, getting bumped once in the mcast code
itself, and again in the common ip output path.  Remove the mcast bump, as its
not needed

Validated by the reporter, with good results
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Reported-by: Claus Jensen <claus.jensen@microsemi.com>
CC: Claus Jensen <claus.jensen@microsemi.com>
CC: David Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/mcast.c

@@ -1651,7 +1651,6 @@ static void mld_sendpack(struct sk_buff *skb)
 	if (!err) {
 		ICMP6MSGOUT_INC_STATS(net, idev, ICMPV6_MLD2_REPORT);
 		ICMP6_INC_STATS(net, idev, ICMP6_MIB_OUTMSGS);
-		IP6_UPD_PO_STATS(net, idev, IPSTATS_MIB_OUTMCAST, payload_len);
 	} else {
 		IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);
 	}
@@ -2015,7 +2014,6 @@ static void igmp6_send(struct in6_addr *addr, struct net_device *dev, int type)
 	if (!err) {
 		ICMP6MSGOUT_INC_STATS(net, idev, type);
 		ICMP6_INC_STATS(net, idev, ICMP6_MIB_OUTMSGS);
-		IP6_UPD_PO_STATS(net, idev, IPSTATS_MIB_OUTMCAST, full_len);
 	} else
 		IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);