RFC: Change gsm_subscriber tmsi from char[17] to u_int32_t

Hey guys, for some historic reason our tmsi is an character array but all places dealing with it treat it as a 4 octet, and according to the spec it is a four octet. I have changed the definition and the code using the tmsi. It can be found in my onwaves.com branch. Does it make sense to switch? z.