TC_e1_crcx_and_dlcx_ep does not pass - move the IPA code out of libosmo-abis
The testcase TC_e1_crcx_and_dlcx_ep can not be executed correctly because it requires a running osmo-e1d but in order to have this available in jenkins this would mean that we need to build the related debian packages with osmo-e1d support, which then creates an impractical dependency to osmo-e1d.
The proper solution is to move the IPA code out of libosmo-abis. Historically that made sense, as the IPA multiplex was first encountered in Abis. But then it was also present in SCCPlite, we started using it for GSUP, and most recently for RSPRO in osmo-remsim. This now means that virtually all osmocom projects depend on libosmo-abis, while all they want is the IPA abstraction. Adding osmo-e1d support to libosmo-abis creates another dependency, and I rally do not want to have to exlpain to an osmo-remsim user why he needs to install an E1 interface driver if he wants to have remote sim functionality. So my plan was to see if we can untangle this somehow without spending two weeks of time on it, and then re-enable the dependency of libosmo-abis to osmo-e1d once nobody (except osmo-mgw and osmo-bsc) depend on libosmo-abis anymore.
See also #2547