sgsn/test: Add test that intercepts gprs_gsup_client_send

This test replaces gprs_gsup_client_send by a custom function, that
emulates a GSUP remote peer by calling gprs_subscr_rx_gsup_message
with responses for all requests. It then executes a full
Attach/Detach cycle.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/tests/sgsn/Makefile.am b/openbsc/tests/sgsn/Makefile.am
index 672b811..c1b5fbd 100644
--- a/openbsc/tests/sgsn/Makefile.am
+++ b/openbsc/tests/sgsn/Makefile.am
@@ -9,7 +9,8 @@
 sgsn_test_LDFLAGS = \
 	-Wl,--wrap=sgsn_update_subscriber_data \
 	-Wl,--wrap=gprs_subscr_request_update_location \
-	-Wl,--wrap=gprs_subscr_request_auth_info
+	-Wl,--wrap=gprs_subscr_request_auth_info \
+	-Wl,--wrap=gprs_gsup_client_send
 
 sgsn_test_LDADD = \
 	$(top_builddir)/src/gprs/gprs_llc_parse.o \