ArduSub: add do_disarm_checks boolean to disarm call

this creates symmetry between arming and disarming, at least as far as
the top-level arm() and disarm() calls are concerned.

ArduSub/AP_Arming_Sub.cpp

@@ -152,14 +152,14 @@ bool AP_Arming_Sub::arm(AP_Arming::Method method, bool do_arming_checks)
     return true;
 }
 
-bool AP_Arming_Sub::disarm(const AP_Arming::Method method)
+bool AP_Arming_Sub::disarm(const AP_Arming::Method method, bool do_disarm_checks)
 {
     // return immediately if we are already disarmed
     if (!sub.motors.armed()) {
         return false;
     }
 
-    if (!AP_Arming::disarm(method)) {
+    if (!AP_Arming::disarm(method, do_disarm_checks)) {
         return false;
     }
 

ArduSub/AP_Arming_Sub.h

@@ -15,7 +15,7 @@ public:
     bool pre_arm_checks(bool display_failure) override;
     bool has_disarm_function() const;
 
-    bool disarm(AP_Arming::Method method) override;
+    bool disarm(AP_Arming::Method method, bool do_disarm_checks=true) override;
     bool arm(AP_Arming::Method method, bool do_arming_checks=true) override;
 
 protected: