selftests: mptcp: lib: use wait_local_port_listen helper

This patch includes net_helper.sh into mptcp_lib.sh, uses the helper
wait_local_port_listen() defined in it to implement the similar mptcp
helper. This can drop some duplicate code.

It looks like this helper from net_helper.sh was originally coming from
MPTCP, but MPTCP selftests have not been updated to use it from this
shared place.

Signed-off-by: Geliang Tang <[email protected]>
Reviewed-by: Matthieu Baerts (NGI0) <[email protected]>
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Link: https://lore.kernel.org/r/20240607-upstream-net-next-20240607-selftests-mptcp-net-lib-v1-6-e36986faac94@kernel.org
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Geliang Tang

tools/testing/selftests/net/mptcp/mptcp_lib.sh

@@ -2,6 +2,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
 . "$(dirname "${0}")/../lib.sh"
+. "$(dirname "${0}")/../net_helper.sh"
 
 readonly KSFT_PASS=0
 readonly KSFT_FAIL=1
@@ -363,20 +364,7 @@ mptcp_lib_check_transfer() {
 
 # $1: ns, $2: port
 mptcp_lib_wait_local_port_listen() {
-	local listener_ns="${1}"
-	local port="${2}"
-
-	local port_hex
-	port_hex="$(printf "%04X" "${port}")"
-
-	local _
-	for _ in $(seq 10); do
-		ip netns exec "${listener_ns}" cat /proc/net/tcp* | \
-			awk "BEGIN {rc=1} {if (\$2 ~ /:${port_hex}\$/ && \$4 ~ /0A/) \
-			     {rc=0; exit}} END {exit rc}" &&
-			break
-		sleep 0.1
-	done
+	wait_local_port_listen "${@}" "tcp"
 }
 
 mptcp_lib_check_output() {