Quash a load of compile warnings

Kevin Lyda writes:
I enclose the following patch which removes all but three of the warnings.  i
don't have any non-linux systems handy to test a fix to the round() function.
but having it return a double should be fine.

It doesn't actually fix anything, it just shuts up -Wall, so it's certainly an
optional type of patch.

ntp_io.c

@@ -184,7 +184,7 @@ read_from_socket(void *anything)
   ReceiveBuffer message;
   int message_length;
   struct sockaddr_in where_from;
-  int from_length;
+  socklen_t from_length;
   unsigned int flags = 0;
   struct timeval now;
   NTP_Remote_Address remote_addr;