cellular support for usb

[heini66]

thxs for adding the cellular support.
it would be great to get support to any device that has enough flash to supprt usb cellular modems.

[blocktrron]

This is a deliberate design decision, as Gluon abstracts the high-level configuration (APN / Username / PIN) to the settings required for the specific modem protocol. Thus we need to know the modem-model when executing gluon-reconfigure.