bsc: release dchan in TC_cbsp_emerg_write_bts_cgi_dchan

A follow-up patch is adding BSC_Tests.f_shutdown_helper() calls to all
CBSP testcases, what makes TC_cbsp_emerg_write_bts_cgi_dchan fail due
to talloc count mismatch.  All dchans need to be released to avoid this.

Change-Id: I8b707c821693f930ab10bd8feea08ba5007da967
diff --git a/bsc/BSC_Tests.ttcn b/bsc/BSC_Tests.ttcn
index c2cf8d3..ed56fc2 100644
--- a/bsc/BSC_Tests.ttcn
+++ b/bsc/BSC_Tests.ttcn
@@ -8257,7 +8257,7 @@
 	BSSAP.send(RAN_Conn_Prim:MSC_CONN_PRIM_DISC_REQ);
 }
 
-private function f_perform_clear_test_ct(DchanTuple dt)
+friend function f_perform_clear_test_ct(DchanTuple dt)
 	runs on test_CT
 {
 	/* Instruct BSC to clear channel */