no IE type included in the message. These information elements are
mandatory, so their actual IE type is known. The improved parse_tlv()
function allows to parse zero, one, or two length-value elements.
(Andreas Eversberg)
* implement TLV type descriptions for NM
* add operational/administrative/availability state keeping logic to abis_nm
* explicitly print all NACK's in abis_nm
* make sure we produce [not just for BS-11] valid channel attributes