mtp: Preserve last modified time of files.

Bug: 6325175
Test: Transfer files
Change-Id: I54af3205575f2bb83c732bb70907f60e0b785e91
Signed-off-by: caozhiyuan <cao.zhiyuan@zte.com.cn>
diff --git a/media/mtp/MtpServer.h b/media/mtp/MtpServer.h
index 64d1b72..08a9e4a 100644
--- a/media/mtp/MtpServer.h
+++ b/media/mtp/MtpServer.h
@@ -78,6 +78,7 @@
     MtpObjectFormat     mSendObjectFormat;
     MtpString           mSendObjectFilePath;
     size_t              mSendObjectFileSize;
+    time_t              mSendObjectModifiedTime;
 
     Mutex               mMutex;