This requires that the SQN field is large enough (8 decimal digits), in
order to do in-place changes to the field in the CSV.
The code has not been properly integrated yet. This patch simply adds
the required functionality but doesn't use it in any way yet.
We now depend on libosmo-asn1-map and libans1c.
we probably should move to a more tree-like data structure than a hash
table. But well, lookup is not the most computationally expensive part
compared to the cryptographic operations.