net: mscc: ocelot: set up the bonding mask in a way that avoids a net_device

Since this code should be called from pure switchdev as well as from
DSA, we must find a way to determine the bonding mask not by looking
directly at the net_device lowers of the bonding interface, since those
could have different private structures.

We keep a pointer to the bonding upper interface, if present, in struct
ocelot_port. Then the bonding mask becomes the bitwise OR of all ports
that have the same bonding upper interface. This adds a duplication of
functionality with the current "lags" array, but the duplication will be
short-lived, since further patches will remove the latter completely.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>