Some system components like VPN need to know how to redact
NetworkCapabilities & LinkProperties that they received from
the system but need to send to third-party applications with
less privilege than themselves. To make sure the redaction is
consistent, expose system API methods to do it that are wired
to the same redaction code used by ConnectivityService.
Bug: 191413541
Test: atest CtsNetTestCases, which includes new CTS for these
Change-Id: Ia3ae4755b5192884c147d6828f96cedac000a25b
c582d50b8e