move various generic IPA related functions to libosmocore

libosmo-abis is about forming A-bis interfaces/lines by means
of E1 or the IPA multiplex (or possibly other link layers).

The IPA multiplex is used in other contexts, such as the Control
interface, or the A interface.  In that context, it makes sense to have
generic IPA related functions in libosmocore.
5 files changed