pjproject: avoid to declare check valid too soon

The relay candidate was declared as suceeded even if not in the valid list.
Because of this, some negotiations were successful but no valid candidates
were given to the app.

Moreover, the connection timeout checks were using the wrong timer. This
avoids to cancel successful negotiations to check a connection timeout.

Finally, some clean is done with this patch

Change-Id: Iacfbf3b9f5faafe1bd05f66157485226761c30bf
Gitlab: #256