Don't update dialog route set from UPDATE response

[nanang]

UPDATE may occur in early dialog and currently dialog route set will be updated upon receiving 200 response of the UPDATE.

RFC3311/UPDATE itself doesn't seem to specify anything about updating dialog route set (in early dialog), however this specification may be applicable here, ​http://tools.ietf.org/html/rfc3261#section-12.2:

   Requests within a dialog MAY contain Record-Route and Contact header
   fields.  However, these requests do not cause the dialog's route set
   to be modified, although they may modify the remote target URI.
   ...
   Target refresh requests only update the dialog's remote target URI,
   and not the route set formed from the Record-Route.

Thanks Brian Walker for the report.

[nanang]

In 4911:

Fix #1781: Don't update dialog route set from UPDATE response.