selftests: forwarding: add a test for local_termination.sh

This tests the capability of switch ports to filter out undesired
traffic. Different drivers are expected to have different capabilities
here (so some may fail and some may pass), yet the test still has some
value, for example to check for regressions.

There are 2 kinds of failures, one is when a packet which should have
been accepted isn't (and that should be fixed), and the other "failure"
(as reported by the test) is when a packet could have been filtered out
(for being unnecessary) yet it was received.

The bridge driver fares particularly badly at this test:

TEST: br0: Unicast IPv4 to primary MAC address                      [ OK ]
TEST: br0: Unicast IPv4 to macvlan MAC address                      [ OK ]
TEST: br0: Unicast IPv4 to unknown MAC address                      [FAIL]
        reception succeeded, but should have failed
TEST: br0: Unicast IPv4 to unknown MAC address, promisc             [ OK ]
TEST: br0: Unicast IPv4 to unknown MAC address, allmulti            [FAIL]
        reception succeeded, but should have failed
TEST: br0: Multicast IPv4 to joined group                           [ OK ]
TEST: br0: Multicast IPv4 to unknown group                          [FAIL]
        reception succeeded, but should have failed
TEST: br0: Multicast IPv4 to unknown group, promisc                 [ OK ]
TEST: br0: Multicast IPv4 to unknown group, allmulti                [ OK ]
TEST: br0: Multicast IPv6 to joined group                           [ OK ]
TEST: br0: Multicast IPv6 to unknown group                          [FAIL]
        reception succeeded, but should have failed
TEST: br0: Multicast IPv6 to unknown group, promisc                 [ OK ]
TEST: br0: Multicast IPv6 to unknown group, allmulti                [ OK ]

mainly because it does not implement IFF_UNICAST_FLT. Yet I still think
having the test (with the failures) is useful in case somebody wants to
tackle that problem in the future, to make an easy before-and-after
comparison.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>