devlink: Move set attribute of devlink_port_attrs to devlink_port

The struct devlink_port_attrs holds the attributes of devlink_port.

The 'set' field is not devlink_port's attribute as opposed to most of the
others.

Move 'set' to be devlink_port's field called 'attrs_set'.

Signed-off-by: Danielle Ratson <danieller@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>