bpf, samples: Use "grep -E" instead of "egrep"

The latest version of grep (3.8+) claims the egrep is now obsolete so the
build now contains warnings that look like:

  egrep: warning: egrep is obsolescent; using grep -E

Fix this up by moving the related file to use "grep -E" instead.
Signed-off-by: NTiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NJiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/1668765001-12477-1-git-send-email-yangtiezhu@loongson.cn

samples/bpf/test_cgrp2_tc.sh

@@ -115,7 +115,7 @@ do_exit() {
     if [ "$DEBUG" == "yes" ] && [ "$MODE" != 'cleanuponly' ]
     then
 	echo "------ DEBUG ------"
-	echo "mount: "; mount | egrep '(cgroup2|bpf)'; echo
+	echo "mount: "; mount | grep -E '(cgroup2|bpf)'; echo
 	echo "$CGRP2_TC_LEAF: "; ls -l $CGRP2_TC_LEAF; echo
 	if [ -d "$BPF_FS_TC_SHARE" ]
 	then