'dumpsys media.metrics -proto #' doesn't lose default

makes sure that using "-proto #" option for dumpsys of the metrics
service doesn't leave the protocol set there; we want it to come
back to the defined default if there is no "-proto #" on subsequent
invocations.

Bug: 69797899
Test: multiple dumpsys invocations
diff --git a/services/mediaanalytics/MediaAnalyticsService.h b/services/mediaanalytics/MediaAnalyticsService.h
index 52e4631..3b34f44 100644
--- a/services/mediaanalytics/MediaAnalyticsService.h
+++ b/services/mediaanalytics/MediaAnalyticsService.h
@@ -125,6 +125,7 @@
 
     // support for generating output
     int mDumpProto;
+    int mDumpProtoDefault;
     String8 dumpQueue(List<MediaAnalyticsItem*> *);
     String8 dumpQueue(List<MediaAnalyticsItem*> *, nsecs_t, const char *only);