network: Add support for QMI modems

network: Add support for QMI modems

QMI is a proprietary interface from Qualcomm which are absolute pioneers
when it comes to interfacing with modems. I don't think there would be
any way to make this any more complicated and bloated.

So, bascially we will put the modem into a raw IP mode which changes the
interface into Point-to-Point mode.

We then configure the provider settings using qmicli. After that, the
modem will try to connect to the provider and obtain an IP address.

We will then start a DHCP client which does not do any DHCP-ing because
implementing that would be too complicated. Instead we do something even
*more* complicated where we would launch a custom script which asks the
modem for the allocated IP address and will configure it into the
device. The DHCP client then reads that IP address from the device and
pretends it came up with it by itself. Such an easy way to do this.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>