netfilter: nfnetlink_hook: missing chain family

The family is relevant for pseudo-families like NFPROTO_INET
otherwise the user needs to rely on the hook function name to
differentiate it from NFPROTO_IPV4 and NFPROTO_IPV6 names.

Add nfnl_hook_chain_desc_attributes instead of using the existing
NFTA_CHAIN_* attributes, since these do not provide a family number.

Fixes: e2cf17d377 ("netfilter: add new hook nfnl subsystem")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nfnetlink_hook.h

@@ -43,6 +43,15 @@ enum nfnl_hook_chain_info_attributes {
 };
 #define NFNLA_HOOK_INFO_MAX (__NFNLA_HOOK_INFO_MAX - 1)
 
+enum nfnl_hook_chain_desc_attributes {
+	NFNLA_CHAIN_UNSPEC,
+	NFNLA_CHAIN_TABLE,
+	NFNLA_CHAIN_FAMILY,
+	NFNLA_CHAIN_NAME,
+	__NFNLA_CHAIN_MAX,
+};
+#define NFNLA_CHAIN_MAX (__NFNLA_CHAIN_MAX - 1)
+
 /**
  * enum nfnl_hook_chaintype - chain type
  *