selftests: mptcp: run mptcp_inq from a clean netns

A new "sandbox" net namespace is available where no other netfilter
rules have been added.

Use this new netns instead of re-using "ns1" and clean it.
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
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

@@ -282,7 +282,7 @@ run_tests()
 
 do_tcpinq_test()
 {
-	ip netns exec "$ns1" ./mptcp_inq "$@"
+	ip netns exec "$ns_sbox" ./mptcp_inq "$@"
 	lret=$?
 	if [ $lret -ne 0 ];then
 		ret=$lret
@@ -298,9 +298,6 @@ do_tcpinq_tests()
 {
 	local lret=0
 
-	ip netns exec "$ns1" iptables -F
-	ip netns exec "$ns1" ip6tables -F
-
 	for args in "-t tcp" "-r tcp"; do
 		do_tcpinq_test $args
 		lret=$?