Allow connection priorities SCHEDULED and URGENT for class 3 connections

Previously these priorities have been rejected in class 3 connection opening.
Now they will be accepted and map to the Explicit DSCP value as set in the QoS-Object.
It is in the responsibility of the connection originator to select appropriate priorities.
URGENT is dedicated to CIP Motion and SCHEDULED shall only be used for Safety-I/O.
Anyway, there is no need to restrict this in the Adapter and all such checks have been removed.