I have made the test proposed, I still recive the same error :)
ofonod: Missing support for TUN/TAP devices
It seems you device doesn't support TUN/TAP. at_gprs_context_probe return -ENODEV,
So it cause the gprs context driver is not set (ofono_gprs_context->driver is NULL).
Any suggestion ?
Remove TUN checking code, in drivers/atmodem/gprs-context.c:at_gprs_context_probe()
Hope it help.