autotest: adjust for reboot-required transmitter-tuning option value

reboot is now required.  Also verify that we are zeroing the DZ

Author: peterbarker

Tools/autotest/arducopter.py

@@ -12683,6 +12683,10 @@ def Ch6TuningWPSpeed(self):
             "AUTO_OPTIONS": 3,
         })
         self.set_rc(6, 2000)
+        self.reboot_sitl()
+
+        # DZ default should be set:
+        self.assert_parameter_value("RC6_DZ", 0)
 
         self.upload_simple_relhome_mission([
             (mavutil.mavlink.MAV_CMD_NAV_TAKEOFF, 0, 0, 20),