Copter: set UARTs non-blocking at end of initialisation

Previously we were setting to non-block after arming but this reduce the
chance of bumping into a NuttX USB driver issue that can cause the uart
to become unresponsive and also makes Copter consistent with Plane

ArduCopter/motors.pde

@@ -139,15 +139,6 @@ static void init_arm_motors()
     gcs_send_text_P(SEVERITY_HIGH, PSTR("ARMING MOTORS"));
 #endif
 
-    // we don't want writes to the serial port to cause us to pause
-    // mid-flight, so set the serial ports non-blocking once we arm
-    // the motors
-    hal.uartA->set_blocking_writes(false);
-    hal.uartC->set_blocking_writes(false);
-    if (hal.uartD != NULL) {
-        hal.uartD->set_blocking_writes(false);
-    }
-
     // Remember Orientation
     // --------------------
     init_simple_bearing();

ArduCopter/system.pde

@@ -278,6 +278,15 @@ static void init_ardupilot()
     Log_Write_Startup();
 #endif
 
+    // we don't want writes to the serial port to cause us to pause
+    // mid-flight, so set the serial ports non-blocking once we are
+    // ready to fly
+    hal.uartA->set_blocking_writes(false);
+    hal.uartC->set_blocking_writes(false);
+    if (hal.uartD != NULL) {
+        hal.uartD->set_blocking_writes(false);
+    }
+
     cliSerial->print_P(PSTR("\nReady to FLY "));
 }