Install the pcuif_proto.h header file

So far, we used to keep a copy of the header file around in
both osmo-pcu and osmo-bts projects.  Before we start introducing
a third copy in openbsc, let's have the osmo-pcu install the header
file and make the other programs use that.

Change-Id: I60976c9be5488256d1ff55fdc5aa548e3705400d
7 files changed