Allows to configure the default realm to be used at the listener side, for all connections.
Realm configuration is currently used by the SASL DIGEST-MD5 authentication. It is optional, but if defined, it must match the realm configuration defined by the SASL login realm value provided by the client peer.
A value to be configured for the realm could be: aspl.es
The value provided will to be copied, so it must be an static string (or at least an string that is deallocated once the vortex library stops its functions).
To get the value configured you must use vortex_listener_get_default_realm.