selftests: net: local_termination: add one more test for VLAN-aware bridges

The current bridge() test is for packet reception on a VLAN-unaware
bridge. Some things are different enough with VLAN-aware bridges that
it's worth renaming this test into vlan_unaware_bridge(), and add a new
vlan_aware_bridge() test.

The two will share the same implementation: bridge() becomes a common
function, which receives $vlan_filtering as an argument. Rename it to
test_bridge() at the same time, because just bridge() pollutes the
global namespace and we cannot invoke the binary with the same name from
the iproute2 package currently.

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