Make NetBlockRandomIPv4 responsible for tracking number of random addrs

targets.h

@@ -100,11 +100,10 @@ public:
   /* Returns true iff the defer buffer is not yet full. */
   bool defer(Target *t);
   void undefer();
+  const char *next_expression();
   bool get_next_host(struct sockaddr_storage *ss, size_t *sslen, struct addrset *exclude_group);
   private:
-  int num_random;
   bool process_next_expression();
-  const char *next_expression();
 };
 
 /* ports is used to pass information about what ports to use for host discovery */