Commands 'ss -M' are used in scripts mptcp_connect.sh, mptcp_join.sh,
and mptcp_sockopt.sh to display only MPTCP sockets. So it must be checked
if ss tool supports MPTCP in these script.

Signed-off-by: Geliang Tang <geliang.tang@linux.dev>
---
 tools/testing/selftests/net/mptcp/mptcp_connect.sh | 6 ++++++
 tools/testing/selftests/net/mptcp/mptcp_join.sh    | 6 ++++++
 tools/testing/selftests/net/mptcp/mptcp_sockopt.sh | 6 ++++++
 3 files changed, 18 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.sh b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
index e19b1fe67408..b554c2e9750e 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_connect.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
@@ -145,6 +145,12 @@ if [ $? -ne 0 ];then
 	exit $ksft_skip
 fi
 
+ss -h | grep -q MPTCP
+if [ $? -ne 0 ];then
+	echo "SKIP: ss tool does not support MPTCP"
+	exit $ksft_skip
+fi
+
 sin=$(mktemp)
 sout=$(mktemp)
 cin=$(mktemp)
diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 7dec65a5ed75..57a9ea9db2ec 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -141,6 +141,12 @@ check_tools()
 		exit $ksft_skip
 	fi
 
+	ss -h | grep -q MPTCP
+	if [ $? -ne 0 ];then
+		echo "SKIP: ss tool does not support MPTCP"
+		exit $ksft_skip
+	fi
+
 	# Use the legacy version if available to support old kernel versions
 	if iptables-legacy -V &> /dev/null; then
 		iptables="iptables-legacy"
diff --git a/tools/testing/selftests/net/mptcp/mptcp_sockopt.sh b/tools/testing/selftests/net/mptcp/mptcp_sockopt.sh
index ff49ee9b9cc2..2c11cad6b607 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_sockopt.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_sockopt.sh
@@ -85,6 +85,12 @@ if [ $? -ne 0 ];then
 	exit $ksft_skip
 fi
 
+ss -h | grep -q MPTCP
+if [ $? -ne 0 ];then
+	echo "SKIP: ss tool does not support MPTCP"
+	exit $ksft_skip
+fi
+
 # Use the legacy version if available to support old kernel versions
 if iptables-legacy -V &> /dev/null; then
 	iptables="iptables-legacy"
-- 
2.35.3