mlxsw: spectrum: Move port SWID set before core port init

During port creation, mlxsw_core_port_init() is called with the front
panel port number and the split port sub-number. Currently, this
information is determined by the driver without firmware assistance.

Subsequent patches are going to query this information from firmware,
but this requires the port to assigned to SWID.

Therefore, move port SWID assignment before mlxsw_core_port_init().

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>