Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 78bfadf..1b3d032 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
  * Home page: