Clarification on registrationExpireTime | webrtc-registration

[teikuran]

Problem description
The current specification for the webrtc-registration may need further clarification regarding how the GW handles the 'registrationExpireTime' when it is explicitly provided by the API consumer.

While the description for regSessionRequest states that if the client omits this field, the server sets the expiry according to its own TTL policy, there is no description about how the GW handles the registrationExpireTime when it is explicitly provided by the API consumer e.g., whehter the GW should strictly follow or ignore a client-provided value that exceeds operator limits.

Expected action
The "Server behaviour" should be mentioned e.g., regarding on the point if GW should respect the request or not and how.