selftests: mptcp: userspace pm remove initial subflow

This patch adds a selftest for userspace PM to remove the initial
subflow.

Use userspace_pm_add_sf() to add a subflow, and pass initial IP address
to userspace_pm_rm_sf() to remove the initial subflow.
Reviewed-by: Matthieu Baerts <matttbe@kernel.org>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20231128-send-net-next-2023107-v4-7-8d6b94150f6b@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -3514,6 +3514,30 @@ userspace_tests()
 		kill_events_pids
 		wait $tests_pid
 	fi
+
+	# userspace pm remove initial subflow
+	if reset_with_events "userspace pm remove initial subflow" &&
+	   continue_if mptcp_lib_has_file '/proc/sys/net/mptcp/pm_type'; then
+		set_userspace_pm $ns2
+		pm_nl_set_limits $ns1 0 1
+		speed=5 \
+			run_tests $ns1 $ns2 10.0.1.1 &
+		local tests_pid=$!
+		wait_mpj $ns2
+		userspace_pm_add_sf $ns2 10.0.3.2 20
+		chk_join_nr 1 1 1
+		chk_mptcp_info subflows 1 subflows 1
+		chk_subflows_total 2 2
+		userspace_pm_rm_sf $ns2 10.0.1.2
+		# we don't look at the counter linked to the RM_ADDR but
+		# to the one linked to the subflows that have been removed
+		chk_rm_nr 0 1
+		chk_rst_nr 0 0 invert
+		chk_mptcp_info subflows 1 subflows 1
+		chk_subflows_total 1 1
+		kill_events_pids
+		wait $tests_pid
+	fi
 }
 
 endpoint_tests()