Add truncate timestamp annotation to DataUsageBytesTransfer

Since buildStatsEvent method is now generated
automatically and adopted after ag/12090439, the
DataUsageBytesTransfer atom needs to be properly annotated to
generate ANNOTATION_ID_TRUNCATE_TIMESTAMP annotation.

Test: m statslog-framework-java-gen
Test: atest UidAtomTests#testDataUsageBytesTransfer

Bug: 160368804
Change-Id: I57f1a60e6fa9af197f5c7da154d55f944cd2383f