We will expose a new 'Ports' property listing all ports currently known by a
given modem. Ports which are not used but are detected as being part of the
modem will be listed with an 'unknown' port type.
This change uses the new 'MMModemPortType' enum and the new 'MMModemPortInfo'
helper struct to handle these values in libmm-glib. The already available
'MMPortType' enum hasn't been re-used for the interface because it contains
values that we don't need (e.g. IGNORED).
The port list is now also included in the modem information command of mmcli:
$ sudo mmcli -m 0
/org/freedesktop/ModemManager1/Modem/0 (device id '97b7b99e3e2bea103880545b619fb05a3cc81b26')
-------------------------
System | device: '/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.4'
| drivers: 'qcserial, qmi_wwan'
| plugin: 'Gobi'
| primary port: 'cdc-wdm0'
| ports: 'ttyUSB0 (qcdm), ttyUSB1 (at), cdc-wdm0 (qmi), wwp0s29u1u4 (net)'
https://bugzilla.gnome.org/show_bug.cgi?id=702678
