selftests/vsock: make wait_for_listener() work even if pipefail is on

Rewrite wait_for_listener()'s pattern matching to avoid tripping the
if-condition when pipefail is on.

awk doesn't gracefully handle SIGPIPE with a non-zero exit code, so grep
exiting upon finding a match causes false-positives when the pipefail
option is used (grep exits, SIGPIPE emits, and awk complains with a
non-zero exit code). Instead, move all of the pattern matching into awk
so that SIGPIPE cannot happen and the correct exit code is returned.

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20251108-vsock-selftests-fixes-and-improvements-v4-2-d5e8d6c87289@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/vsock/vmtest.sh

@@ -251,9 +251,11 @@ wait_for_listener()
 
 	# for tcp protocol additionally check the socket state
 	[ "${protocol}" = "tcp" ] && pattern="${pattern}0A"
+
 	for i in $(seq "${max_intervals}"); do
-		if awk '{print $2" "$4}' /proc/net/"${protocol}"* | \
-		   grep -q "${pattern}"; then
+		if awk -v pattern="${pattern}" \
+			'BEGIN {rc=1} $2" "$4 ~ pattern {rc=0} END {exit rc}' \
+			/proc/net/"${protocol}"*; then
 			break
 		fi
 		sleep "${interval}"