Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/net/switchdev/Makefile b/net/switchdev/Makefile
index 5ed63ed..bd69a31 100644
--- a/net/switchdev/Makefile
+++ b/net/switchdev/Makefile
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
 #
 # Makefile for the Switch device API
 #