net: napi_hash_del() returns a boolean status

napi_hash_del() will soon be used from both drivers (if they want)
or core networking stack.

Callers are responsibles to ensure an RCU grace period is respected
before freeing napi structure : napi_hash_del() can signal if
this RCU grace period is needed or not.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 838935d..e5c33b2 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -474,9 +474,10 @@
  *	@napi: napi context
  *
  * Warning: caller must observe rcu grace period
- * before freeing memory containing @napi
+ * before freeing memory containing @napi, if
+ * this function returns true.
  */
-void napi_hash_del(struct napi_struct *napi);
+bool napi_hash_del(struct napi_struct *napi);
 
 /**
  *	napi_disable - prevent NAPI from scheduling