gimbal: only reset protocol on destruction (#2283)

Don't destruct the found protocol on each discovery. Otherwise, we lose
all subscriptions when a timeout occurs.

Longer term, we'll probably just want to remove the v1 logic to simplify
this.

Signed-off-by: Julian Oes <julian@oes.ch>

src/mavsdk/plugins/gimbal/gimbal_impl.cpp

@@ -34,7 +34,11 @@ void GimbalImpl::init()
         this);
 }
 
-void GimbalImpl::deinit() {}
+void GimbalImpl::deinit()
+{
+    _gimbal_protocol.reset(nullptr);
+    _system_impl->unregister_all_mavlink_message_handlers(this);
+}
 
 void GimbalImpl::enable()
 {
@@ -50,7 +54,7 @@ void GimbalImpl::enable()
 
 void GimbalImpl::disable()
 {
-    _gimbal_protocol.reset(nullptr);
+    _system_impl->unregister_timeout_handler(_protocol_cookie);
 }
 
 void GimbalImpl::receive_protocol_timeout()