pingpong: Optimised the endofresp() function

Reworked the pp->endofresp() function so that the conndata, line and
line length are passed down to it just as with Curl_client_write()
rather than each implementation of the function having to query
these values.

Additionally changed the int return type to bool as this is more
representative of the function's usage.

lib/pingpong.h

@@ -64,7 +64,7 @@ struct pingpong {
 
   CURLcode (*statemach_act)(struct connectdata *conn);
 
-  int (*endofresp)(struct pingpong *pp, int *code);
+  bool (*endofresp)(struct connectdata *conn, char *ptr, size_t len, int *code);
 };
 
 /*