bts: More complete AGCH / IMM.ASS testing

The existing test simply sent 1000 messages via RSL without checking
what actually arrived on the radio interface, or without
expecting/counting any RSL DELETE IND.

Let's fix this by introducing test sending IMM.ASS at three different
rates, with related expectations in terms of nubmer of IMM.ASS arriving
on Um vs. RSL DELETE IND arriving at BSC.

Change-Id: Ib6043b76ba1d7aaff107bb612f63b5a747d8720c
Related: OS#2990
Related: SYS#2695
diff --git a/library/RSL_Types.ttcn b/library/RSL_Types.ttcn
index b81bbbd..3804d40 100644
--- a/library/RSL_Types.ttcn
+++ b/library/RSL_Types.ttcn
@@ -1394,6 +1394,15 @@
 			t_RSL_IE(RSL_IE_FULL_IMM_ASS_INFO, RSL_IE_Body:{full_imm_ass_info := ts_RSL_LV(imm_ass)})
 		}
 	}
+	template RSL_Message tr_RSL_DELETE_IND(template octetstring imm_ass := ?, template uint3_t tn) := {
+		msg_disc := tr_RSL_MsgDisc(RSL_MDISC_CCHAN, false),
+		msg_type := RSL_MT_DELETE_IND,
+		ies := {
+			tr_RSL_IE(RSL_IE_Body:{chan_nr := t_RslChanNr_PCH_AGCH(tn)}),
+			tr_RSL_IE(RSL_IE_Body:{full_imm_ass_info := tr_RSL_LV(imm_ass)}),
+			*
+		}
+	}
 
 	/* 8.5.5 BSC -> BTS */
 	template RSL_Message tr_RSL_PAGING_CMD(template octetstring identity, template uint3_t tn := ?) := {