ISDN/PPP: clean up ipppd_write() and ipppd_ioctl()

plus other small cleanups, in particular getting rid of
isdn_ppp_{receive,send}_ccp() and calling into the CCP code directly.

drivers/isdn/i4l/isdn_ppp.h

@@ -27,5 +27,3 @@ int
 isdn_ppp_strip_proto(struct sk_buff *skb);
 
 #define IPPP_MAX_HEADER 10
-
-