netfilter: ctnetlink: fix missing CTA_NAT_SEQ_UNSPEC

This patch fixes an inconsistency in nfnetlink_conntrack.h that
I introduced myself. The problem is that CTA_NAT_SEQ_UNSPEC is
missing from enum ctattr_natseq. This inconsistency may lead to
problems in the message parsing in userspace (if the message
contains the CTA_NAT_SEQ_* attributes, of course).

This patch breaks backward compatibility, however, the only known
client of this code is libnetfilter_conntrack which indeed crashes
because it assumes the existence of CTA_NAT_SEQ_UNSPEC to do
the parsing.

The CTA_NAT_SEQ_* attributes were introduced in 2.6.25.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter/nfnetlink_conntrack.h

@@ -141,6 +141,7 @@ enum ctattr_protonat {
 #define CTA_PROTONAT_MAX (__CTA_PROTONAT_MAX - 1)
 
 enum ctattr_natseq {
+	CTA_NAT_SEQ_UNSPEC,
 	CTA_NAT_SEQ_CORRECTION_POS,
 	CTA_NAT_SEQ_OFFSET_BEFORE,
 	CTA_NAT_SEQ_OFFSET_AFTER,