selftests: forwarding: Allow running specific tests

Similar to commit a511858c75 ("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>

tools/testing/selftests/net/forwarding/router.sh

@@ -1,6 +1,7 @@
 #!/bin/bash
 # SPDX-License-Identifier: GPL-2.0
 
+ALL_TESTS="ping_ipv4 ping_ipv6"
 NUM_NETIFS=4
 source lib.sh
 
@@ -114,12 +115,21 @@ cleanup()
 	vrf_cleanup
 }
 
+ping_ipv4()
+{
+	ping_test $h1 198.51.100.2
+}
+
+ping_ipv6()
+{
+	ping6_test $h1 2001:db8:2::2
+}
+
 trap cleanup EXIT
 
 setup_prepare
 setup_wait
 
-ping_test $h1 198.51.100.2
-ping6_test $h1 2001:db8:2::2
+tests_run
 
 exit $EXIT_STATUS