Hi Alexander,
about your commit on openbsc, merged as 6cacc56d: libgtp should not be a prerequisite for OAP. OAP is a rather simple protocol built on an IPA connection and doesn't really relate to GTP at all.
So if your build of OAP was dependent on libgtp, that's a bug, and probably my fault.
Could you please verify / indicate the failure you saw so we/I can fix it?
Thanks!
~Neels