net: dsa: felix: support FDB entries on offloaded LAG interfaces

This adds the logic in the Felix DSA driver and Ocelot switch library.
For Ocelot switches, the DEST_IDX that is the output of the MAC table
lookup is a logical port (equal to physical port, if no LAG is used, or
a dynamically allocated number otherwise). The allocation we have in
place for LAG IDs is different from DSA's, so we can't use that:
- DSA allocates a continuous range of LAG IDs starting from 1
- Ocelot appears to require that physical ports and LAG IDs are in the
  same space of [0, num_phys_ports), and additionally, ports that aren't
  in a LAG must have physical port id == logical port id

The implication is that an FDB entry towards a LAG might need to be
deleted and reinstalled when the LAG ID changes.

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