Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/kernel/bpf/tnum.c b/kernel/bpf/tnum.c
index 938d412..ca52b96 100644
--- a/kernel/bpf/tnum.c
+++ b/kernel/bpf/tnum.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /* tnum: tracked (or tristate) numbers
  *
  * A tnum tracks knowledge about the bits of a value.  Each bit can be either