NCPInstanceBase: Fix warning on `set_flags()`
NCPInstanceBase: Fix warning on `set_flags()`

abtink/wpantund,openthread/wpantund,abtink/wpantund,openthread/wpantund,aeliot/wpantund,aeliot/wpantund,aeliot/wpantund,abtink/wpantund,openthread/wpantund,openthread/wpantund,abtink/wpantund,aeliot/wpantund