opts/weightdevice.go and opts/throttledevice.go had no tests, unlike the
sibling opts. Add table-driven coverage for ValidateWeightDevice,
ValidateThrottleBpsDevice, ValidateThrottleIOpsDevice and the Set/GetList
paths, including boundary (weight 0/10/1000/overflow) and error cases.
Signed-off-by: Nikolaus Schuetz <nikolauspschuetz@gmail.com>