sgsn: Add 'acl-only' authentication policy

Currently the VTY 'auth-policy' command results in setting or clearing
the acl_enabled flag. This also enables the matching of the MCC/MNC
prefix of the IMSI.

This patch adds an additional policy 'acl-only' which disables the
MCC/MNC matching and relies on the ACL only.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/gprs/sgsn_main.c b/openbsc/src/gprs/sgsn_main.c
index d8e01ff..c7c852d 100644
--- a/openbsc/src/gprs/sgsn_main.c
+++ b/openbsc/src/gprs/sgsn_main.c
@@ -78,7 +78,7 @@
 	.config_file = "osmo_sgsn.cfg",
 	.cfg = {
 		.gtp_statedir = "./",
-		.acl_enabled = 1,
+		.auth_policy = SGSN_AUTH_POLICY_CLOSED,
 	},
 };
 struct sgsn_instance *sgsn = &sgsn_inst;