Fix : extension provider is string type
Changed type of extension provider from list to string (values separated by comma) Tested and results: obuspa -c set Device.Services.VoiceService.1.CallControl.Extension.1.Provider Device.Services.VoiceService.1.DECT.Portable.2,Device.Services.VoiceService.1.DECT.Portable.1 Device.Services.VoiceService.1.CallControl.Extension.1.Provider => Device.Services.VoiceService.1.DECT.Portable.2,Device.Services.VoiceService.1.DECT.Portable.1
uci values: option provider '030444B976,030444B9BA'
obuspa -c set Device.Services.VoiceService.1.CallControl.Extension.4.Provider Device.Services.VoiceService.1.POTS.FXS.1 uci values: option provider 'fxs1'