selftests: forwarding: Allow running specific tests

Similar to commit a511858c7536 ("selftests: fib_tests: Allow user to run
a specific test"), allow user to run only a subset of the tests using
the TESTS environment variable.

This is useful when not all the tests can pass on a given system.

Example:
# export TESTS="ping_ipv4 ping_ipv6"
# ./bridge_vlan_aware.sh
TEST: ping					[PASS]
TEST: ping6					[PASS]

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/tools/testing/selftests/net/forwarding/lib.sh b/tools/testing/selftests/net/forwarding/lib.sh
index a066ca5..061c87b 100644
--- a/tools/testing/selftests/net/forwarding/lib.sh
+++ b/tools/testing/selftests/net/forwarding/lib.sh
@@ -477,6 +477,15 @@
 	   action drop
 }
 
+tests_run()
+{
+	local current_test
+
+	for current_test in ${TESTS:-$ALL_TESTS}; do
+		$current_test
+	done
+}
+
 ##############################################################################
 # Tests