library/GSM_RR_Types.ttcn: fix: IA Rest Octets may have optional padding

According to 3GPP TS 04.08 (version 7.21.0), section 10.5.2.16 and
table 10.5.45, IA Rest Octets IE may contain spare bits. Let's add
an optional field 'pad' to record 'IaRestOctets'.

NOTE: somehow this change crashes my TITAN runtime:

  dec_GsmRrMessage(): Stream before decoding: '2D063F100FE3673A096B0000C800300B2B2B2B2B2B2B2B'O
  *** Error in `././PCU_Tests': malloc(): memory corruption: 0x000000000074a790 ***

while the recent version works just fine.

Change-Id: Ifdcdcf50709fcc03195cb8ef6092977e26f910ec
diff --git a/library/GSM_RR_Types.ttcn b/library/GSM_RR_Types.ttcn
index 627f78f..f313e23 100644
--- a/library/GSM_RR_Types.ttcn
+++ b/library/GSM_RR_Types.ttcn
@@ -543,7 +543,8 @@
 		IaRestOctLL	ll optional,
 		IaRestOctLH	lh optional,
 		IaRestOctHL	hl optional,
-		IaRestOctHH	hh optional
+		IaRestOctHH	hh optional,
+		bitstring	pad optional
 	} with {
 		variant (ll) "PRESENCE(presence = '00'B)"
 		variant (lh) "PRESENCE(presence = '01'B)"