Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/net/ipv4/tcp_scalable.c b/net/ipv4/tcp_scalable.c
index addc122..471571e 100644
--- a/net/ipv4/tcp_scalable.c
+++ b/net/ipv4/tcp_scalable.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /* Tom Kelly's Scalable TCP
  *
  * See http://www.deneholme.net/tom/scalable/