Fix android.media.cts.MediaPlayerFlakyNetworkTest failure

Added mDisconnectLock to seperate it from mLock, used for protecting
mDataSource, mHttpSource and mDisconnected in order that disconnect()
won't be blocked by mLock.

Bug: 133900877
Test: android.media.cts.MediaPlayerFlakyNetworkTest
Change-Id: I15693c0a61f898aad4035d0fa55c8af25de4fc96
diff --git a/media/libmediaplayerservice/nuplayer/GenericSource.h b/media/libmediaplayerservice/nuplayer/GenericSource.h
index 065cac1..4d1905d 100644
--- a/media/libmediaplayerservice/nuplayer/GenericSource.h
+++ b/media/libmediaplayerservice/nuplayer/GenericSource.h
@@ -170,6 +170,7 @@
     sp<ABuffer> mGlobalTimedText;
 
     mutable Mutex mLock;
+    mutable Mutex mDisconnectLock; // Protects mDataSource, mHttpSource and mDisconnected
 
     sp<ALooper> mLooper;