allow arbitrary bytes in Global Title (GT), a.k.a. the VLR,SGSN's identification towards the HLR
osmo-msc and osmo-sgsn send IPA_IDTAG_SERNR identifications to osmo-hlr of the form "MSC-00-00-00-00-00-00".
We've already enlarged the vlr_number and sgsn_number fields in osmo-hlr's subscriber struct to make room for this.
However, the real Global Title to identify an entity like the MSC should be allowed to contain arbitrary bytes and lengths.
Particularly, in osmo-hlr's luop, the luop->peer is just a pointer and needs a length.
Furthermore we should not expect nul termination, as we currently do, for proper GT support.
We should also adjust osmo-hlr's database scheme for arbitrary GT blobs.