ipv6: log src and dst along with "udp checksum is 0"

These info messages are rather pointless without any means to identify
the source of the bogus packets.  Logging the src and dst addresses and
ports may help a bit.

Cc: Joe Perches <joe@perches.com>
Signed-off-by: NBjørn Mork <bjorn@mork.no>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_checksum.c

@@ -79,7 +79,9 @@ int udp6_csum_init(struct sk_buff *skb, struct udphdr *uh, int proto)
 		/* RFC 2460 section 8.1 says that we SHOULD log
 		   this error. Well, it is reasonable.
 		 */
-		LIMIT_NETDEBUG(KERN_INFO "IPv6: udp checksum is 0\n");
+		LIMIT_NETDEBUG(KERN_INFO "IPv6: udp checksum is 0 for [%pI6c]:%u->[%pI6c]:%u\n",
+			       &ipv6_hdr(skb)->saddr, ntohs(uh->source),
+			       &ipv6_hdr(skb)->daddr, ntohs(uh->dest));
 		return 1;
 	}
 	if (skb->ip_summed == CHECKSUM_COMPLETE &&