library/GSM_RestOctets: add partial definition of SI 6 Rest Octets

Change-Id: I5aeed4986820a71f761f21b57c87782d3000293f
diff --git a/library/GSM_SystemInformation.ttcn b/library/GSM_SystemInformation.ttcn
index 86ff817..53c36c8 100644
--- a/library/GSM_SystemInformation.ttcn
+++ b/library/GSM_SystemInformation.ttcn
@@ -193,7 +193,7 @@
 		LocationAreaIdentification	lai,
 		CellOptionsSacch		cell_options,
 		BIT8				ncc_permitted,
-		RestOctets			rest_octets length(0..7)
+		SI6RestOctets			rest_octets
 	} with { variant "" };
 
 	/* 44.018 9.1.43a */