gbproxy: Fix parser to accept GSM 24.008 Attach Req messages

Currently the parse expects a 'MS network capability' IE with
2 <= length <= 3 which is compliant to GSM 04.08, 9.4.1  but not to
GSM 24.008, 9.4.1 which specifies 3 <= length <= 9. Thus the parser
rejects messages with a length >= 4 (including length field).

This patch relaxes the length check to accept either range by
requiring 2 <= length <= 9.

Ticket: OW#1258
Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/gprs/gprs_gb_parse.c b/openbsc/src/gprs/gprs_gb_parse.c
index a0a4469..db40e97 100644
--- a/openbsc/src/gprs/gprs_gb_parse.c
+++ b/openbsc/src/gprs/gprs_gb_parse.c
@@ -155,7 +155,7 @@
 
 	/* Skip MS network capability */
 	if (lv_shift(&data, &data_len, NULL, &value_len) <= 0 ||
-	    value_len < 1 || value_len > 2)
+	    value_len < 1 || value_len > 8)
 		/* invalid */
 		return 0;;