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/libmgcp/mgcp_vty.c b/openbsc/src/libmgcp/mgcp_vty.c
index 69984ee..833908a 100644
--- a/openbsc/src/libmgcp/mgcp_vty.c
+++ b/openbsc/src/libmgcp/mgcp_vty.c
@@ -898,7 +898,8 @@
 	return 0;
 }
 
-int mgcp_parse_config(const char *config_file, struct mgcp_config *cfg)
+int mgcp_parse_config(const char *config_file, struct mgcp_config *cfg,
+		      enum mgcp_role role)
 {
 	int rc;
 	struct mgcp_trunk_config *trunk;
@@ -935,6 +936,7 @@
 			return -1;
 		}
 	}
+	cfg->role = role;
 
 	return 0;
 }