Revert the public API changes in "Refactor StructCapUser{Header,Data} and StructLinger for API review"

Revert the changes in https://r.android.com/1689750 partially.

Remove StructLinger from public APIs, but becomes @CorePlatformApi(STABLE)

As discussed with API council, it's too late to make the APIs
public in Android S. Thus, moving this back @CorePlatformApi.

Bug: 183513856
Test: m droid
Change-Id: Ic3e8a99b3844445286332677ed0f38c9b1850fb0
5 files changed