mlxsw: Use u16 for local_port field instead of u8

Currently, local_port field is saved as u8, which means that maximum 256
ports can be used.

As preparation for Spectrum-4, which will support more than 256 ports,
local_port field should be extended.

Save local_port as u16 to allow use of additional ports.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>