Rover now honours the Param1 setting of a time in seconds for a
NAV_WAYPOINT and the Rover will loiter at that waypoint for that
period of time.
Note that as soon as the Rover reaches that waypoint the loiter timer
will start. If you enter a different mode during this time (HOLD for
instance) the timer resets. If you then switch back to AUTO
mode and the Rover returns to that waypoint it will wait for the
loiter time configured in param1.
