Update package of DataConnectionStats

DataConnectStats is now created from BatteryStatsService because
it actually receive necessaary signal and update to BSS. It's
better to move the class into a package that is more related
BSS, so update the package into com.android.server.am.

This commit also fixes some style issues.

Bug: 171183530
Test: m
Change-Id: I61c28599a03a66bf0d83d78076a0791ff63f48cc