selftests: mptcp: sockopt: skip TCP_INQ checks if not supported

Selftests are supposed to run on any kernels, including the old ones not
supporting all MPTCP features.

One of them is TCP_INQ cmsg support introduced in commit 2c9e77659a
("mptcp: add TCP_INQ cmsg support").

It is possible to look for "mptcp_ioctl" in kallsyms because it was
needed to introduce the mentioned feature. We can skip these tests and
not set TCPINQ option if the feature is not supported.

Link: https://github.com/multipath-tcp/mptcp_net-next/issues/368
Fixes: 5cbd886ce2 ("selftests: mptcp: add TCP_INQ support")
Cc: stable@vger.kernel.org
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -187,9 +187,14 @@ do_transfer()
 		local_addr="0.0.0.0"
 	fi
 
+	cmsg="TIMESTAMPNS"
+	if mptcp_lib_kallsyms_has "mptcp_ioctl$"; then
+		cmsg+=",TCPINQ"
+	fi
+
 	timeout ${timeout_test} \
 		ip netns exec ${listener_ns} \
-			$mptcp_connect -t ${timeout_poll} -l -M 1 -p $port -s ${srv_proto} -c TIMESTAMPNS,TCPINQ \
+			$mptcp_connect -t ${timeout_poll} -l -M 1 -p $port -s ${srv_proto} -c "${cmsg}" \
 				${local_addr} < "$sin" > "$sout" &
 	local spid=$!
 
@@ -197,7 +202,7 @@ do_transfer()
 
 	timeout ${timeout_test} \
 		ip netns exec ${connector_ns} \
-			$mptcp_connect -t ${timeout_poll} -M 2 -p $port -s ${cl_proto} -c TIMESTAMPNS,TCPINQ \
+			$mptcp_connect -t ${timeout_poll} -M 2 -p $port -s ${cl_proto} -c "${cmsg}" \
 				$connect_addr < "$cin" > "$cout" &
 
 	local cpid=$!
@@ -313,6 +318,11 @@ do_tcpinq_tests()
 {
 	local lret=0
 
+	if ! mptcp_lib_kallsyms_has "mptcp_ioctl$"; then
+		echo "INFO: TCP_INQ not supported: SKIP"
+		return
+	fi
+
 	local args
 	for args in "-t tcp" "-r tcp"; do
 		do_tcpinq_test $args