selftests: net: mscc: ocelot: add a test for egress VLAN modification

For this test we are exercising the VCAP ES0 block's ability to match on
a packet with a given VLAN ID, and push an ES0 TAG A with a VID derived
from VID_A_VAL plus the classified VLAN.

$eth3.200 is the generator port
$eth0 is the bridged DUT port that receives
$eth1 is the bridged DUT port that forwards and rewrites VID 200 to 300
      on egress via VCAP ES0
$eth2 is the port that receives from the DUT port $eth1

Since the egress rewriting happens outside the bridging service, VID 300
does not need to be in the bridge VLAN table of $eth1.

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