Sub: Hide Circle Nav parameters from user

ArduSub/Parameters.cpp

@@ -750,9 +750,11 @@ const AP_Param::Info Sub::var_info[] = {
     // @Path: ../libraries/AC_WPNav/AC_WPNav.cpp
     GOBJECT(wp_nav, "WPNAV_",       AC_WPNav),
 
+#if CIRCLE_NAV_ENABLED == ENABLED
     // @Group: CIRCLE_
     // @Path: ../libraries/AC_WPNav/AC_Circle.cpp
     GOBJECT(circle_nav, "CIRCLE_",  AC_Circle),
+#endif
 
     // @Group: ATC_
 	// @Path: ../libraries/AC_AttitudeControl/AC_AttitudeControl.cpp,../libraries/AC_AttitudeControl/AC_AttitudeControl_Multi.cpp

ArduSub/config.h

@@ -86,6 +86,14 @@
    #   define RC_FAST_SPEED 490
 #endif
 
+//////////////////////////////////////////////////////////////////////////////
+// Circle Nav parameters
+//
+
+#ifndef CIRCLE_NAV_ENABLED
+# define CIRCLE_NAV_ENABLED DISABLED
+#endif
+
 //////////////////////////////////////////////////////////////////////////////
 // Channel 6 Tuning
 //