[NETFILTER]: xt_pkttype: Add explicit check for IPv4

In the PACKET_LOOPBACK case, the skb data was always interpreted as
IPv4, but that is not valid for IPv6, obviously. Fix this by adding an
extra condition to check for AF_INET.
Signed-off-by: NJan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/netfilter/xt_pkttype.c

@@ -31,7 +31,8 @@ pkttype_mt(const struct sk_buff *skb, const struct net_device *in,
 	const struct xt_pkttype_info *info = matchinfo;
 
 	if (skb->pkt_type == PACKET_LOOPBACK)
-		type = ipv4_is_multicast(ip_hdr(skb)->daddr)
+		type = match->family == AF_INET &&
+		       ipv4_is_multicast(ip_hdr(skb)->daddr)
 			? PACKET_MULTICAST
 			: PACKET_BROADCAST;
 	else