CDD: add requirement for always-on VPN opt-out.

Require UI implementations to observe the always-on VPN opt-out manifest
flag in app manifest, if such implementation exists.

See VpnService.SERVICE_META_DATA_SUPPORTS_ALWAYS_ON

Bug: 65561270
Test: N/A
Change-Id: Ie0b5ea506affbec0ab3b0268c2539bc0184721aa
1 file changed