Copter: init_arm_motors calls pre-arm checks

This reduces a small amount of duplicated code in the pilot initiated
arming and GCS initiated arming functions

ArduCopter/GCS_Mavlink.pde

@@ -1162,16 +1162,10 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
 
         case MAV_CMD_COMPONENT_ARM_DISARM:
             if (packet.param1 == 1.0f) {
-                // run pre_arm_checks and arm_checks and display failures
-                if(pre_arm_checks(true) && arm_checks(true, true)) {
-                    if (init_arm_motors()) {
-                        result = MAV_RESULT_ACCEPTED;
-                    } else {
-                        AP_Notify::flags.arming_failed = true;  // init_arm_motors function will reset flag back to false
-                        result = MAV_RESULT_UNSUPPORTED;
-                    }
-                }else{
-                    AP_Notify::flags.arming_failed = true;  // init_arm_motors function will reset flag back to false
+                // attempt to arm and return success or failure
+                if (init_arm_motors(false)) {
+                    result = MAV_RESULT_ACCEPTED;
+                } else {
                     result = MAV_RESULT_UNSUPPORTED;
                 }
             } else if (packet.param1 == 0.0f && (mode_has_manual_throttle(control_mode) || ap.land_complete))  {

ArduCopter/motors.pde

@@ -31,17 +31,9 @@ static void arm_motors_check()
 
         // arm the motors and configure for flight
         if (arming_counter == ARM_DELAY && !motors.armed()) {
-            // run pre-arm-checks and display failures
-            if(pre_arm_checks(true) && arm_checks(true,false)) {
-                if (!init_arm_motors()) {
-                    // reset arming counter if arming fail
-                    arming_counter = 0;
-                    AP_Notify::flags.arming_failed = true;
-                }
-            }else{
-                // reset arming counter if pre-arm checks fail
+            // reset arming counter if arming fail
+            if (!init_arm_motors(false)) {
                 arming_counter = 0;
-                AP_Notify::flags.arming_failed = true;
             }
         }
 
@@ -100,8 +92,8 @@ static void auto_disarm_check()
 }
 
 // init_arm_motors - performs arming process including initialisation of barometer and gyros
-//  returns false in the unlikely case that arming fails (because of a gyro calibration failure)
-static bool init_arm_motors()
+//  returns false if arming failed because of pre-arm checks, arming checks or a gyro calibration failure
+static bool init_arm_motors(bool arming_from_gcs)
 {
 	// arming marker
     // Flag used to track if we have armed the motors the first time.
@@ -109,6 +101,12 @@ static bool init_arm_motors()
     // which calibrates the IMU
     static bool did_ground_start = false;
 
+    // run pre-arm-checks and display failures
+    if(!pre_arm_checks(true) || !arm_checks(true, arming_from_gcs)) {
+        AP_Notify::flags.arming_failed = true;
+        return false;
+    }
+
     // disable cpu failsafe because initialising everything takes a while
     failsafe_disable();