bsc: add TC_imm_ass_pre_chan_ack

Add tests for the new early IMM ASS feature in osmo-bsc:
  'immediate-assignment (post-chan-ack|pre-chan-ack)'

Related: 0b44493d3de03d2750527e224df67b473fe39f93 (osmo-bsc)
Related: SYS#5559
Change-Id: If71f4562d532b6c5faf55f5fd073449a8a137ebf
diff --git a/library/GSM_RR_Types.ttcn b/library/GSM_RR_Types.ttcn
index 78db7a5..f7b00e1 100644
--- a/library/GSM_RR_Types.ttcn
+++ b/library/GSM_RR_Types.ttcn
@@ -1038,7 +1038,8 @@
 	template GsmRrMessage tr_IMM_ASS(template uint8_t ra := ?, template GsmFrameNumber fn := ?,
 					 template TimingAdvance ta := ?,
 					 template ChannelDescription ch_desc := ?,
-					 template MobileAllocationLV ma := ?) := {
+					 template MobileAllocationLV ma := ?,
+					 template PageMode page_mode := PAGE_MODE_NORMAL) := {
 		header := t_RrHeader(IMMEDIATE_ASSIGNMENT, ?),
 		payload := {
 			imm_ass := {
@@ -1048,7 +1049,7 @@
 					downlink := false,
 					tbf := false
 				},
-				page_mode := PAGE_MODE_NORMAL,
+				page_mode := page_mode,
 				chan_desc := ch_desc,
 				pkt_chan_desc := omit,
 				req_ref := tr_compute_ReqRef(ra, fn),