Patches - add support for mobile-originated USSD

Hello again, More patches - these two (combined) add support for mobile-originated USSD. The demonstration application, implemented in ussd.c, is that sending *#100# to the network will display your 5-digit extension. It's not 100% finished - I've tested it on 6 handsets, 5 of them work perfectly, but the 6th (Samsung i520) doesn't seem to receive the response, so more experimenting to be done... Best regards to all, Mike H.