selftests: mptcp: pm nl: skip fullmesh flag 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 the fullmesh flag that can be given to the MPTCP
in-kernel path-manager and introduced in commit 2843ff6f ("mptcp:
remote addresses fullmesh").

If the flag is not visible in the dump after having set it, we don't
check the content. Note that if we expect to have this feature and
SELFTESTS_MPTCP_LIB_EXPECT_ALL_FEATURES env var is set to 1, we always
check the content to avoid regressions.

Link: https://github.com/multipath-tcp/mptcp_net-next/issues/368
Fixes: 6da1dfdd ("selftests: mptcp: add set_flags tests in pm_netlink.sh")
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/pm_netlink.sh

@@ -178,14 +178,19 @@ subflow,backup 10.0.1.1" "set flags (backup)"
 ip netns exec $ns1 ./pm_nl_ctl set 10.0.1.1 flags nobackup
 check "ip netns exec $ns1 ./pm_nl_ctl dump" "id 1 flags \
 subflow 10.0.1.1" "          (nobackup)"
+
+# fullmesh support has been added later
 ip netns exec $ns1 ./pm_nl_ctl set id 1 flags fullmesh
-check "ip netns exec $ns1 ./pm_nl_ctl dump" "id 1 flags \
+if ip netns exec $ns1 ./pm_nl_ctl dump | grep -q "fullmesh" ||
+   mptcp_lib_expect_all_features; then
+	check "ip netns exec $ns1 ./pm_nl_ctl dump" "id 1 flags \
 subflow,fullmesh 10.0.1.1" "          (fullmesh)"
-ip netns exec $ns1 ./pm_nl_ctl set id 1 flags nofullmesh
-check "ip netns exec $ns1 ./pm_nl_ctl dump" "id 1 flags \
+	ip netns exec $ns1 ./pm_nl_ctl set id 1 flags nofullmesh
+	check "ip netns exec $ns1 ./pm_nl_ctl dump" "id 1 flags \
 subflow 10.0.1.1" "          (nofullmesh)"
-ip netns exec $ns1 ./pm_nl_ctl set id 1 flags backup,fullmesh
-check "ip netns exec $ns1 ./pm_nl_ctl dump" "id 1 flags \
+	ip netns exec $ns1 ./pm_nl_ctl set id 1 flags backup,fullmesh
+	check "ip netns exec $ns1 ./pm_nl_ctl dump" "id 1 flags \
 subflow,backup,fullmesh 10.0.1.1" "          (backup,fullmesh)"
+fi
 
 exit $ret