[NETFILTER] ctnetlink: ICMP ID is not mandatory

The ID is only required by ICMP type 8 (echo), so it's not
mandatory for all sort of ICMP connections. This patch makes
mandatory only the type and the code for ICMP netlink messages.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/ip_conntrack_proto_icmp.c

@@ -296,8 +296,7 @@ static int icmp_nfattr_to_tuple(struct nfattr *tb[],
 				struct ip_conntrack_tuple *tuple)
 {
 	if (!tb[CTA_PROTO_ICMP_TYPE-1]
-	    || !tb[CTA_PROTO_ICMP_CODE-1]
-	    || !tb[CTA_PROTO_ICMP_ID-1])
+	    || !tb[CTA_PROTO_ICMP_CODE-1])
 		return -1;
 
 	tuple->dst.u.icmp.type =