rhashtable: provide len to obj_hashfn

nftables sets will be converted to use so called setextensions, moving
the key to a non-fixed position. To hash it, the obj_hashfn must be used,
however it so far doesn't receive the length parameter.

Pass the key length to obj_hashfn() and convert existing users.

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

net/netlink/af_netlink.c

@@ -3127,7 +3127,7 @@ static struct pernet_operations __net_initdata netlink_net_ops = {
 	.exit = netlink_net_exit,
 };
 
-static inline u32 netlink_hash(const void *data, u32 seed)
+static inline u32 netlink_hash(const void *data, u32 len, u32 seed)
 {
 	const struct netlink_sock *nlk = data;
 	struct netlink_compare_arg arg;