aq_fw2x_thermal_arm() reached for a copper PHY register that the fibre
parts do not implement, so arming failed on every init and printed a
warning for a capability the hardware cannot have. Return ENOTSUP when
the firmware does not advertise a temperature sensor, matching
aq_fw2x_get_temp(), and warn only for a genuine failure.
Signed-off-by: Nick Price <nprice@FreeBSD.org>