MSCHAP was written the old-way, with all functions declared non static in
header, independent of their local or global scope status. Same for local
constants. Reworked in a more mordern way.
We are going to need ppp_pcb* in MSCHAP and MSCHAPv2 for MPPE for
int mppe_keys_set, u_char mppe_send_key and u_char mppe_recv_key
which are currently global variable which must be moved to ppp_pcb.
