batman-adv: Use rcu_dereference_protected by update-side

Usually rcu_dereference isn't necessary in situations were the
RCU-protected data structure cannot change, but sparse and lockdep still
need a similar functionality for analysis. rcu_dereference_protected
implements the reduced version which should be used to support the
dynamic and static analysis.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index e0052cf..a3fbfb5 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -138,7 +138,7 @@
 	if (new_hard_iface && !atomic_inc_not_zero(&new_hard_iface->refcount))
 		new_hard_iface = NULL;
 
-	curr_hard_iface = bat_priv->primary_if;
+	curr_hard_iface = rcu_dereference_protected(bat_priv->primary_if, 1);
 	rcu_assign_pointer(bat_priv->primary_if, new_hard_iface);
 
 	if (curr_hard_iface)