Mobile broadband connection for ppp

I’ve managed to port the netcfg connection for ppp on a mobile broadband device to netctl, and added an example profile. The original scripts were based off[1]—I don’t know who wrote that, and documentation on AT commands is ridiculously scarce and/or outdated, especially for USB dongle modems.

I’ve tested it on my own system, and it seems to work. The code is more proof-of-concept than anything else, but I’m happy to maintain this connection type to keep it up-to-date. It could probably do with some tidying up; maybe splitting the `ppp_up()` function into separate functions to create the two runtime files.

[1] https://wiki.archlinux.org/index.php/3G_and_GPRS_modems_with_pppd