GenericSource: release mLock when operation might take long time.

This allows disconnect() to be done quickly in order to not block
reset() in mediaplayer.
Test: pass android.media.cts.MediaPlayerFlakyNetworkTest
Bug: 68954085

Change-Id: I3ebfef66098066f2169d9946c417fe530cc1fa1b
diff --git a/media/libmediaplayerservice/nuplayer/GenericSource.h b/media/libmediaplayerservice/nuplayer/GenericSource.h
index f4debc1..807b620 100644
--- a/media/libmediaplayerservice/nuplayer/GenericSource.h
+++ b/media/libmediaplayerservice/nuplayer/GenericSource.h
@@ -158,6 +158,7 @@
     int64_t mOffset;
     int64_t mLength;
 
+    bool mDisconnected;
     sp<DataSource> mDataSource;
     sp<NuCachedSource2> mCachedSource;
     sp<DataSource> mHttpSource;