Feng Tu reported that curl -w did wrong on TFTP transfers in

bug report #1715394 (http://curl.haxx.se/bug/view.cgi?id=1715394), and the
transfer-related info "variables" were indeed overwritten with zeroes wrongly
and have now been adjusted. The upload size still isn't accurate.

lib/transfer.c

@@ -1792,9 +1792,11 @@ Transfer(struct connectdata *conn)
   struct Curl_transfer_keeper *k = &data->reqdata.keep;
   bool done=FALSE;
 
-  if(!(conn->protocol & PROT_FILE)) {
-    /* Only do this if we are not transferring FILE:, since the file: treatment
-       is different*/
+  if(!(conn->protocol & (PROT_FILE|PROT_TFTP))) {
+    /* Only do this if we are not transferring FILE or TFTP, since those
+       transfers are treated differently. They do their entire transfers in
+       the DO function and just returns from this. That is ugly indeed.
+    */
     Curl_readwrite_init(conn);
     Curl_pre_readwrite(conn);
   }