selftests: mptcp: join: reset failing links

Best to always reset this env var before each test to avoid surprising
behaviour depending on the order tests are running.

Also clearly set it for the last failing links test is also needed when
only this test is executed.
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -23,6 +23,8 @@ declare -A all_tests
 TEST_COUNT=0
 nr_blank=40
 
+export FAILING_LINKS=""
+
 # generated using "nfbpf_compile '(ip && (ip[54] & 0xf0) == 0x30) ||
 #				  (ip6 && (ip6[74] & 0xf0) == 0x30)'"
 CBPF_MPTCP_SUBOPTION_ADD_ADDR="14,
@@ -63,6 +65,7 @@ init_partial()
 
 	check_invert=0
 	validate_checksum=$checksum
+	FAILING_LINKS=""
 
 	#  ns1              ns2
 	# ns1eth1    ns2eth1
@@ -1618,7 +1621,7 @@ link_failure_tests()
 	pm_nl_set_limits $ns1 0 2
 	pm_nl_add_endpoint $ns1 10.0.2.1 dev ns1eth2 flags signal
 	pm_nl_set_limits $ns2 1 2
-	export FAILING_LINKS="1"
+	FAILING_LINKS="1"
 	pm_nl_add_endpoint $ns2 10.0.3.2 dev ns2eth3 flags subflow,backup
 	run_tests $ns1 $ns2 10.0.1.1 1
 	chk_join_nr "backup subflow unused, link failure" 2 2 2
@@ -1633,7 +1636,7 @@ link_failure_tests()
 	pm_nl_add_endpoint $ns1 10.0.2.1 dev ns1eth2 flags signal
 	pm_nl_set_limits $ns2 1 2
 	pm_nl_add_endpoint $ns2 10.0.3.2 dev ns2eth3 flags subflow,backup
-	export FAILING_LINKS="1 2"
+	FAILING_LINKS="1 2"
 	run_tests $ns1 $ns2 10.0.1.1 1
 	chk_join_nr "backup flow used, multi links fail" 2 2 2
 	chk_add_nr 1 1
@@ -1648,6 +1651,7 @@ link_failure_tests()
 	pm_nl_add_endpoint $ns1 10.0.2.1 dev ns1eth2 flags signal
 	pm_nl_set_limits $ns2 1 3
 	pm_nl_add_endpoint $ns2 10.0.3.2 dev ns2eth3 flags subflow,backup
+	FAILING_LINKS="1 2"
 	run_tests $ns1 $ns2 10.0.1.1 2
 	chk_join_nr "backup flow used, bidi, link failure" 2 2 2
 	chk_add_nr 1 1