[HSL] initial support for the HSL 2.75G Femtocell

The HSL Femtocell seems to be a poor man implementation of the
ip.access Abis/IP protocol, but cutting corners wherever possible.

We try to workaround those corners wherever possible...
diff --git a/openbsc/src/libbsc/Makefile.am b/openbsc/src/libbsc/Makefile.am
index 91be7fa..de76929 100644
--- a/openbsc/src/libbsc/Makefile.am
+++ b/openbsc/src/libbsc/Makefile.am
@@ -8,7 +8,11 @@
 			abis_om2000.c abis_om2000_vty.c \
 			abis_rsl.c bsc_rll.c \
 			paging.c \
-			bts_ericsson_rbs2000.c bts_ipaccess_nanobts.c bts_siemens_bs11.c bts_unknown.c \
+			bts_ericsson_rbs2000.c \
+			bts_ipaccess_nanobts.c \
+			bts_siemens_bs11.c \
+			bts_hsl_femtocell.c \
+			bts_unknown.c \
 			chan_alloc.c \
 			gsm_subscriber_base.c \
 			handover_decision.c handover_logic.c meas_rep.c \