b432bc75e5
This is only necessary when learning the NAT64 prefix from the RA, because if the NAT64 prefix is learned from DNS, the DNS resolver already knows the prefix and automatically enables DNS64 synthesis. The DNS resolver needs to be informed of the prefix any time clat is running on a prefix learned from an RA. This is simple to implement: just set the prefix when starting clat if prefix discovery is not running, and clear the prefix when stopping clat if prefix discovery was not running. This ensures that the prefix is cleared iff it was set. Bug: 156914456 Test: new unit test coverage Change-Id: If8ad2d30712a6df3e207c8d3e8a129705242191e