rhashtable: Annotate RCU locking of walkers

Fixes the following sparse warnings:

lib/rhashtable.c:767:5: warning: context imbalance in 'rhashtable_walk_start' - wrong count at exit
lib/rhashtable.c:849:6: warning: context imbalance in 'rhashtable_walk_stop' - unexpected unlock

Fixes: f2dba9c6ff0d ("rhashtable: Introduce rhashtable_walk_*")
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index c523d3a..eae26a6 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -760,6 +760,7 @@
  * by calling rhashtable_walk_next.
  */
 int rhashtable_walk_start(struct rhashtable_iter *iter)
+	__acquires(RCU)
 {
 	struct rhashtable *ht = iter->ht;
 
@@ -847,6 +848,7 @@
  * Finish a hash table walk.
  */
 void rhashtable_walk_stop(struct rhashtable_iter *iter)
+	__releases(RCU)
 {
 	struct rhashtable *ht;
 	struct bucket_table *tbl = iter->walker->tbl;