gbproxy: Introduce TC_overload

When the SGSN is sending an OVERLOAD message, we expect that to
propagate down to every BSS on the other side.

Change-Id: Ic61fabd9c633bcb3f256fe7aa5834e66cc66a4fb
diff --git a/library/BSSGP_Emulation.ttcnpp b/library/BSSGP_Emulation.ttcnpp
index d747ca2..e3ad9fe 100644
--- a/library/BSSGP_Emulation.ttcnpp
+++ b/library/BSSGP_Emulation.ttcnpp
@@ -302,7 +302,7 @@
 private template PDU_BSSGP tr_GLOBAL := (
 	{pDU_BSSGP_SUSPEND:=?}, {pDU_BSSGP_SUSPEND_ACK:=?}, {pDU_BSSGP_SUSPEND_NACK:=?},
 	{pDU_BSSGP_RESUME:=?}, {pDU_BSSGP_RESUME_ACK:=?}, {pDU_BSSGP_RESUME_NACK:=?},
-	{pDU_BSSGP_SGSN_INVOKE_TRACE:=?}
+	{pDU_BSSGP_SGSN_INVOKE_TRACE:=?}, {pDU_BSSGP_OVERLOAD:=?}
 );
 
 /* We are in BVC_S_UNBLOCKED state */