libmgcp: add enum mgcp_role

This enum indicates if the mgcp is running on the BSC or the BSC-NAT.
diff --git a/openbsc/src/osmo-bsc_nat/bsc_nat.c b/openbsc/src/osmo-bsc_nat/bsc_nat.c
index 897c657..1eac983 100644
--- a/openbsc/src/osmo-bsc_nat/bsc_nat.c
+++ b/openbsc/src/osmo-bsc_nat/bsc_nat.c
@@ -1515,7 +1515,7 @@
 
 	/* init vty and parse */
 	telnet_init(tall_bsc_ctx, NULL, 4244);
-	if (mgcp_parse_config(config_file, nat->mgcp_cfg) < 0) {
+	if (mgcp_parse_config(config_file, nat->mgcp_cfg, MGCP_BSC_NAT) < 0) {
 		fprintf(stderr, "Failed to parse the config file: '%s'\n", config_file);
 		return -3;
 	}