macosx: use hotkeys for apple remote volume control

partial revert of 9929cc94
Until we find a better solution. As discussed on ML.

modules/gui/macosx/intf.m

@@ -1060,10 +1060,12 @@ static VLCMain *_o_sharedMainInstance = nil;
                 [[VLCCoreInteraction sharedInstance] backward];
                 break;
             case kRemoteButtonVolume_Plus_Hold:
-                [[VLCCoreInteraction sharedInstance] volumeUp];
+                if (p_intf)
+                    var_SetInteger(p_intf->p_libvlc, "key-action", ACTIONID_VOL_UP);
                 break;
             case kRemoteButtonVolume_Minus_Hold:
-                [[VLCCoreInteraction sharedInstance] volumeDown];
+                if (p_intf)
+                    var_SetInteger(p_intf->p_libvlc, "key-action", ACTIONID_VOL_DOWN);
                 break;
         }
         if (b_remote_button_hold) {
@@ -1097,13 +1099,15 @@ static VLCMain *_o_sharedMainInstance = nil;
             if (config_GetInt(VLCIntf, "macosx-appleremote-sysvol"))
                 [NSSound increaseSystemVolume];
             else
-                [[VLCCoreInteraction sharedInstance] volumeUp];
+                if (p_intf)
+                    var_SetInteger(p_intf->p_libvlc, "key-action", ACTIONID_VOL_UP);
             break;
         case kRemoteButtonVolume_Minus:
             if (config_GetInt(VLCIntf, "macosx-appleremote-sysvol"))
                 [NSSound decreaseSystemVolume];
             else
-                [[VLCCoreInteraction sharedInstance] volumeDown];
+                if (p_intf)
+                    var_SetInteger(p_intf->p_libvlc, "key-action", ACTIONID_VOL_DOWN);
             break;
         case kRemoteButtonRight:
             if (config_GetInt(VLCIntf, "macosx-appleremote-prevnext"))