selftests: net: mscc: ocelot: add test for VLAN modify action

Create a test that changes a VLAN ID from 200 to 300.

We also need to modify the preferences of the filters installed for the
other rules so that they are unique, because we now install the "tc-vlan
modify" filter in VCAP IS1 only temporarily, and we need to perform the
deletion by filter preference number.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>