make address flag optional

use unspecified address as default value.
this will extract a routable IP to listen on and advertise

cmd/lotus-seal-worker/main.go

@@ -95,6 +95,7 @@ var runCmd = &cli.Command{
 		&cli.StringFlag{
 			Name:  "address",
 			Usage: "Locally reachable address",
+			Value: "0.0.0.0",
 		},
 		&cli.BoolFlag{
 			Name:  "no-local-storage",
@@ -123,10 +124,6 @@ var runCmd = &cli.Command{
 			}
 		}
 
-		if cctx.String("address") == "" {
-			return xerrors.Errorf("--address flag is required")
-		}
-
 		// Connect to storage-miner
 		var nodeApi api.StorageMiner
 		var closer func()