A new endpoint using the IP of the initial subflow has been recently
added to increase the code coverage. But it breaks the test when using
old kernels not having commit 86e39e04482b ("mptcp: keep track of local
endpoint still available for each msk"), e.g. on v5.15.

Similar to commit d4c81bbb8600 ("selftests: mptcp: join: support local
endpoint being tracked or not"), it is possible to add the new endpoint
conditionally, by checking if "mptcp_pm_subflow_check_next" is present
in kallsyms: this is not directly linked to the commit introducing this
symbol but for the parent one which is linked anyway. So we can know in
advance what will be the expected behaviour, and add the new endpoint
only when it makes sense to do so.

Fixes: 4878f9f8421f ("selftests: mptcp: join: validate fullmesh endp on 1st sf")
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 3564cd06643c..e8d0a01b4144 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -3130,7 +3130,9 @@ fullmesh_tests()
 		pm_nl_set_limits $ns1 1 3
 		pm_nl_set_limits $ns2 1 3
 		pm_nl_add_endpoint $ns1 10.0.2.1 flags signal
-		pm_nl_add_endpoint $ns2 10.0.1.2 flags subflow,fullmesh
+		if mptcp_lib_kallsyms_has "mptcp_pm_subflow_check_next$"; then
+			pm_nl_add_endpoint $ns2 10.0.1.2 flags subflow,fullmesh
+		fi
 		fullmesh=1 speed=slow \
 			run_tests $ns1 $ns2 10.0.1.1
 		chk_join_nr 3 3 3

-- 
2.45.2