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>

include/linux/rhashtable.h

@@ -88,7 +88,7 @@ struct rhashtable_compare_arg {
 };
 
 typedef u32 (*rht_hashfn_t)(const void *data, u32 len, u32 seed);
-typedef u32 (*rht_obj_hashfn_t)(const void *data, u32 seed);
+typedef u32 (*rht_obj_hashfn_t)(const void *data, u32 len, u32 seed);
 typedef int (*rht_obj_cmpfn_t)(struct rhashtable_compare_arg *arg,
 			       const void *obj);
 
@@ -242,7 +242,9 @@ static inline unsigned int rht_head_hashfn(
 	const char *ptr = rht_obj(ht, he);
 
 	return likely(params.obj_hashfn) ?
-	       rht_bucket_index(tbl, params.obj_hashfn(ptr, tbl->hash_rnd)) :
+	       rht_bucket_index(tbl, params.obj_hashfn(ptr, params.key_len ?:
+							    ht->p.key_len,
+						       tbl->hash_rnd)) :
 	       rht_key_hashfn(ht, tbl, ptr + params.key_offset, params);
 }