The 'modemmanager' uses the 'dbus'. Status information can be retrieved
with the 'mmcli' command, this can also be output in json format.
This commit adds a new 'ubus' backend with which this information can
be easily accessed via ubus.
* ubus call modemmanager info
* ubus call modemmanager dump
Signed-off-by: Florian Eckert <fe@dev.tdt.de>
