Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/net/ipv4/tcp_htcp.c b/net/ipv4/tcp_htcp.c
index 082d479..88e1f01 100644
--- a/net/ipv4/tcp_htcp.c
+++ b/net/ipv4/tcp_htcp.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * H-TCP congestion control. The algorithm is detailed in:
  * R.N.Shorten, D.J.Leith: