Sub: show frame class as part of banner

Similar to how Copter does in its equivalent method.

frame type is not used on Sub ATM

ArduSub/GCS_Mavlink.cpp

@@ -76,6 +76,12 @@ MAV_STATE GCS_MAVLINK_Sub::vehicle_system_status() const
     return MAV_STATE_STANDBY;
 }
 
+void GCS_MAVLINK_Sub::send_banner()
+{
+    GCS_MAVLINK::send_banner();
+    send_text(MAV_SEVERITY_INFO, "Frame: %s", sub.motors.get_frame_string());
+}
+
 void GCS_MAVLINK_Sub::send_nav_controller_output() const
 {
     const Vector3f &targets = sub.attitude_control.get_att_target_euler_cd();

ArduSub/GCS_Mavlink.h

@@ -32,6 +32,8 @@ protected:
     bool set_home_to_current_location(bool lock) override WARN_IF_UNUSED;
     bool set_home(const Location& loc, bool lock) override WARN_IF_UNUSED;
 
+    void send_banner() override;
+
     void send_nav_controller_output() const override;
     void send_pid_tuning() override;