[patch 0/6] Initial patches for gatchat PPP support

These patches implement PPP support for gatchat. They're not complete, but are useful enough to play with if anyone wants to. I included a patch to gsmdial which allows you to invoke the PPP routines after the CONNECT callback. This patch will create a TUN interface, which you will then have to manually configure using the IP Address and DNS information that is output by gsmdial to stdout. There are many items yet to be done, mostly they fall into these categories: * clean exit and Link Loss path * Cleanup and deallocate memory properly * Implement Error path (Configure-Reject etc). I tested this on the AT&T sierra modem, but not with any other modem. I appreciate your feedback.