The filegroups here were set up without an explicit path. As a result,
the files within were incorrectly considered part of the
"src_frameworkcommon.android.net.utils" package by droidstubs'
filter_packages filter (and thus not fed into droidstubs).
This CL fixes the filegroups by adding an explicit path to where the
package tree starts for each of them, such that the path-based
package filter in droidstubs can work correctly.
Also @hide the classes which otherwise would now be considered exposed
API by droidstubs.
Bug: 151160048
Test: make checkapi
Change-Id: I969fc9846294a42554233cffda725797ee0185f4
0607dd9a16