NG_NAS: Fix QoS_Rule type and template definitions

With previous approach TTCN-3 titan would decode QoS_Rule records
wrongly, (eg. as "modify" instead of "new") due to lack of TAG/CROSSTAG
definitions in the union.
Moreover, having a union of lists of PacketFilter made applying LENGTOHF
on numOfPacketFilters difficult too, which also broke dec/enc.

Re-arrange the QoS_Rule into several subtypes based on operation field,
since each operation really defines a lot of stuff, like which
fields are present, etc.