netfilter: nft_hash: add missing NFTA_HASH_OFFSET's nla_policy

Missing the nla_policy description will also miss the validation check
in kernel.

Fixes: 70ca767e ("netfilter: nft_hash: Add hash offset value")
Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_hash.c

@@ -44,6 +44,7 @@ static const struct nla_policy nft_hash_policy[NFTA_HASH_MAX + 1] = {
 	[NFTA_HASH_LEN]		= { .type = NLA_U32 },
 	[NFTA_HASH_MODULUS]	= { .type = NLA_U32 },
 	[NFTA_HASH_SEED]	= { .type = NLA_U32 },
+	[NFTA_HASH_OFFSET]	= { .type = NLA_U32 },
 };
 
 static int nft_hash_init(const struct nft_ctx *ctx,