sgsn: use gtp_clear_queues() when reset sgsn state

Allow ttcn3 to flush the gtp queue between each test.
Fixes ttcn3 test SGSN_Tests.TC_attach_pdp_act_deact_mt_t3395_expire

Change-Id: I49d70cb7abe5cbe92ea68882fa68eccec0e79586
diff --git a/src/gprs/sgsn_vty.c b/src/gprs/sgsn_vty.c
index 057be9f..154e576 100644
--- a/src/gprs/sgsn_vty.c
+++ b/src/gprs/sgsn_vty.c
@@ -823,6 +823,9 @@
 	bssgp_flush_all_queues();
 	vty_out(vty, "Flushed all BSSGPs queues.%s", VTY_NEWLINE);
 
+	gtp_clear_queues(sgsn->gsn);
+	vty_out(vty, "Restarted connection to GGSN.%s", VTY_NEWLINE);
+
 	/* remove all queues to bssgp */
 	return CMD_SUCCESS;
 }