netfilter: uapi: correct UNTRACKED conntrack state bit number

nft_ct exposes this bit to userspace. This used to be

#define NF_CT_STATE_UNTRACKED_BIT (1 << (IP_CT_NUMBER + 1))
(IP_CT_NUMBER is 5, so this was 0x40)

.. but this got changed to 8 (0x100) when the untracked object got removed.
Replace this with a literal 6 to prevent further incompatible changes
in case IP_CT_NUMBER ever increases.

Fixes: cc41c84b7e7f2 ("netfilter: kill the fake untracked conntrack objects")
Reported-by: Li Shuang <[e-mail]>
Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/uapi/linux/netfilter/nf_conntrack_common.h

···
 
 #define NF_CT_STATE_INVALID_BIT			(1 << 0)
 #define NF_CT_STATE_BIT(ctinfo)			(1 << ((ctinfo) % IP_CT_IS_REPLY + 1))
-#define NF_CT_STATE_UNTRACKED_BIT		(1 << (IP_CT_UNTRACKED + 1))
+#define NF_CT_STATE_UNTRACKED_BIT		(1 << 6)
 
 /* Bitset representing status of connection. */
 enum ip_conntrack_status {