Bypass VPN lockdown for clat initialization

This allows clat to initialize properly when VPNs are configured
with "Block connections without VPN", rather than to error out with
"no IPv6 addresses were available for clat".

This issue primarily affects particular mobile networks configured
with NAT64 (without direct IPv4 connectivity).

Bug: 255040839
Change-Id: I4a8ee0295e0f5d1e330f7529856347b8bd10360c
6 files changed