net: dsa: felix: bring the NPI port indirection for host MDBs to surface

For symmetry with host FDBs where the indirection is now handled outside
the ocelot switch lib, do the same for host MDB entries. The only caller
of the ocelot switch lib which uses the NPI port is the Felix DSA driver.

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