sgsn: Integrate the GSUP client into the SGSN

This commit adds GSUP client configuration (via VTY), connection set
up, and real message sending.

The following configuration commands are added:

 - gsup remote-ip A.B.C.D            set server IP address
 - gsup remote-port PORT             set server TCP port

Ticket: OW#1338
Sponsored-by: On-Waves ehf
diff --git a/openbsc/tests/sgsn/Makefile.am b/openbsc/tests/sgsn/Makefile.am
index c8dccfe..70e0924 100644
--- a/openbsc/tests/sgsn/Makefile.am
+++ b/openbsc/tests/sgsn/Makefile.am
@@ -22,9 +22,11 @@
 	$(top_builddir)/src/gprs/sgsn_libgtp.o \
 	$(top_builddir)/src/gprs/sgsn_auth.o \
 	$(top_builddir)/src/gprs/gprs_gsup_messages.o \
+	$(top_builddir)/src/gprs/gprs_gsup_client.o \
 	$(top_builddir)/src/gprs/gprs_utils.o \
 	$(top_builddir)/src/gprs/gprs_subscriber.o \
 	$(top_builddir)/src/libcommon/libcommon.a \
+	$(LIBOSMOABIS_LIBS) \
 	$(LIBOSMOCORE_LIBS) \
 	$(LIBOSMOGSM_LIBS) \
 	$(LIBOSMOGB_LIBS) \