Review Andy: Spot and reject I-CSCF to I-CSCF loops

This fix spots the case where the S-CSCF returned on a lookup from the I-CSCF resolves to be the I-CSCF itself (or one from the same domain) and explicitly rejects it with a loop detect response (482), rather than relying on Max Forwards logic catching the loop, as this is an "expected" error case in the scenario where the cluster has been misconfigured with the I-CSCF and S-CSCF ports reversed.