This is a back-pocket solution only, to ensure that VpnManager
privileged clients can temporarily rely on IPv6 UDP encap if on
certain carriers IPv4 UDP and IPv6 ESP cannot provide acceptable
performance and battery life.
For these reasons IPv6 UDP encap is not a public or system API
and is triggered by passing a port greater than 65535 to the
existing openUdpEncapsulationSocket API.
Bug: 259001350
Test: new CTS tests
Change-Id: I02e0566ba910a300dda6a589cd265a3360add40c
b38fef8333