ModemStatus enum is missing values for Remote Manager connect/disconnect

[mikewadsten]

On XBee Wi-Fi and XBee Cellular devices, modem status frames with values 0xE and 0xF (Remote Manager connected and disconnected, respectively) will be output when the Remote Manager connection is established or is dropped.

This library does not understand those values, and so in the logs we see messages such as:

2017-11-22 10:44:32,510: digi.xbee.reader: DEBUG: /dev/xbibRECEIVED    OperatingMode.API_MODE7E 00 02 8A 0E 67                                 
2017-11-22 10:44:32,511: digi.xbee.reader: INFO: /dev/xbibRECEIVED    MODEM STATUSNone              ModemStatus.UNKNOWN

[rubenmoral]

Thanks @mikewadsten, I've just added the missing modem statuses.