Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/include/net/ax25.h b/include/net/ax25.h
index 3f9aea8..8b7eb46 100644
--- a/include/net/ax25.h
+++ b/include/net/ax25.h
@@ -201,6 +201,18 @@
 
 void __ax25_put_route(ax25_route *ax25_rt);
 
+extern rwlock_t ax25_route_lock;
+
+static inline void ax25_route_lock_use(void)
+{
+	read_lock(&ax25_route_lock);
+}
+
+static inline void ax25_route_lock_unuse(void)
+{
+	read_unlock(&ax25_route_lock);
+}
+
 static inline void ax25_put_route(ax25_route *ax25_rt)
 {
 	if (refcount_dec_and_test(&ax25_rt->refcount))