Allows to get the associated serverName value under which the connection is working.
The serverName value is a centric concept inside BEEP and defines under which name is acting the connection. In general, this value is used to implement resource separation based on the serverName configured.
A key concept is that the serverName value is negociated, accepted and fixed for the rest of the session on the first successful channel created on the connection. Once done, no diferent serverName can be negociated.