selftests: mptcp: allow more slack for slow test-case

A test-case is frequently failing on some extremely slow VMs.
The mptcp transfer completes before the script is able to do
all the required PM manipulation.

Address the issue in the simplest possible way, making the
transfer even more slow.

Additionally dump more info in case of failures, to help debugging
similar problems in the future and init dump_stats var.

Fixes: e274f71540 ("selftests: mptcp: add subflow limits test-cases")
Cc: stable@vger.kernel.org
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/323
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -1694,6 +1694,7 @@ chk_subflow_nr()
 	local subflow_nr=$3
 	local cnt1
 	local cnt2
+	local dump_stats
 
 	if [ -n "${need_title}" ]; then
 		printf "%03u %-36s %s" "${TEST_COUNT}" "${TEST_NAME}" "${msg}"
@@ -1711,7 +1712,12 @@ chk_subflow_nr()
 		echo "[ ok ]"
 	fi
 
-	[ "${dump_stats}" = 1 ] && ( ss -N $ns1 -tOni ; ss -N $ns1 -tOni | grep token; ip -n $ns1 mptcp endpoint )
+	if [ "${dump_stats}" = 1 ]; then
+		ss -N $ns1 -tOni
+		ss -N $ns1 -tOni | grep token
+		ip -n $ns1 mptcp endpoint
+		dump_stats
+	fi
 }
 
 chk_link_usage()
@@ -3069,7 +3075,7 @@ endpoint_tests()
 		pm_nl_set_limits $ns1 1 1
 		pm_nl_set_limits $ns2 1 1
 		pm_nl_add_endpoint $ns2 10.0.2.2 id 2 dev ns2eth2 flags subflow
-		run_tests $ns1 $ns2 10.0.1.1 4 0 0 slow &
+		run_tests $ns1 $ns2 10.0.1.1 4 0 0 speed_20 &
 
 		wait_mpj $ns2
 		pm_nl_del_endpoint $ns2 2 10.0.2.2