netfilter: nft_compat: fix hook validation for non-base chains

Set hook_mask to zero for non-base chains, otherwise people may hit
bogus errors from the xt_check_target() and xt_check_match() when
validating the uninitialized hook_mask.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_compat.c

@@ -95,6 +95,8 @@ nft_target_set_tgchk_param(struct xt_tgchk_param *par,
 		const struct nf_hook_ops *ops = &basechain->ops[0];
 
 		par->hook_mask = 1 << ops->hooknum;
+	} else {
+		par->hook_mask = 0;
 	}
 	par->family	= ctx->afi->family;
 }
@@ -293,6 +295,8 @@ nft_match_set_mtchk_param(struct xt_mtchk_param *par, const struct nft_ctx *ctx,
 		const struct nf_hook_ops *ops = &basechain->ops[0];
 
 		par->hook_mask = 1 << ops->hooknum;
+	} else {
+		par->hook_mask = 0;
 	}
 	par->family	= ctx->afi->family;
 }