Changes

Drop libosmo-abis cond dep together with examples/lapd-over-datagram

libosmo-netif should never depend on libosmo-abis, since it provides
interfaces way more generic than libosmo-abis.
libosmo-abis will in the near future use libosmo-netif's stream APIs, so
break the circular dependency here.
The lapd-over-datagram-* examples will be moved to libosmo-abis since
lapd stuff is defined there.

Change-Id: I13d6e88158f6d9ce017986283183ee9c2cc68cae