add basic unixsocket support

Allow to connect to a unix socket for communicating with LAPD.

Change-Id: Ia5723b09a5c68a0505829dc732def981e60a907a
diff --git a/include/Makefile.am b/include/Makefile.am
index 16fa506..2048520 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -3,4 +3,5 @@
 nobase_include_HEADERS = osmocom/abis/ipa.h osmocom/abis/trau_frame.h	\
  osmocom/abis/ipa_proxy.h osmocom/abis/ipaccess.h osmocom/abis/abis.h	\
  osmocom/abis/subchan_demux.h osmocom/abis/e1_input.h			\
- osmocom/abis/lapd.h osmocom/abis/lapd_pcap.h osmocom/trau/osmo_ortp.h
+ osmocom/abis/lapd.h osmocom/abis/lapd_pcap.h osmocom/trau/osmo_ortp.h	\
+ osmocom/abis/unixsocket_proto.h