Force specifying sanitized/not sanitized in caps from agent

To make sure anyone using the capabilities originally from
the agent have to know what they're dealing with, make the
member private and make accessors that spell out explicitly
the important parts.

This is the last step towards addressing the leftover
comment from aosp/1958906.

Bug: 238139913
Test: FrameworksNetTests CtsNetTestCases
Change-Id: I9fc1986c59726212acfc2ad921745c8bbc424035
3 files changed