Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/samples/bpf/tcp_basertt_kern.c b/samples/bpf/tcp_basertt_kern.c
index 4bf4fc5..9dba48c 100644
--- a/samples/bpf/tcp_basertt_kern.c
+++ b/samples/bpf/tcp_basertt_kern.c
@@ -7,7 +7,7 @@
  * BPF program to set base_rtt to 80us when host is running TCP-NV and
  * both hosts are in the same datacenter (as determined by IPv6 prefix).
  *
- * Use load_sock_ops to load this BPF program.
+ * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
  */
 
 #include <uapi/linux/bpf.h>
@@ -21,13 +21,6 @@
 
 #define DEBUG 1
 
-#define bpf_printk(fmt, ...)					\
-({								\
-	       char ____fmt[] = fmt;				\
-	       bpf_trace_printk(____fmt, sizeof(____fmt),	\
-				##__VA_ARGS__);			\
-})
-
 SEC("sockops")
 int bpf_basertt(struct bpf_sock_ops *skops)
 {