net: dsa: introduce a separate cross-chip notifier type for host FDBs

DSA treats some bridge FDB entries by trapping them to the CPU port.
Currently, the only class of such entries are FDB addresses learnt by
the software bridge on a foreign interface. However there are many more
to be added:

- FDB entries with the is_local flag (for termination) added by the
  bridge on the user ports (typically containing the MAC address of the
  bridge port)
- FDB entries pointing towards the bridge net device (for termination).
  Typically these contain the MAC address of the bridge net device.
- Static FDB entries installed on a foreign interface that is in the
  same bridge with a DSA user port.

The reason why a separate cross-chip notifier for host FDBs is justified
compared to normal FDBs is the same as in the case of host MDBs: the
cross-chip notifier matching function in switch.c should avoid
installing these entries on routing ports that route towards the
targeted switch, but not towards the CPU. This is required in order to
have proper support for H-like multi-chip topologies.

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