Bug #48427 UDN: Forbid vulnerable GET_DN for VERSION >= 3

UDL using PROTOCOL_3 must no longer use GET_DN but WAIT_DN - if it is
still used this is a protocol violation. UDL simply will not get an
answer.

When UCRV 'notifier/protocol/version is set to 3, any old client still
using PROTOCOL_2 will get rejected while negotiating the protocol
version, so it is asserted that "version >= network_procotol_version".