Use proper grpc schema (unix:file) for unix sockets.

Signed-off-by: Piotr Tabor <ptab@google.com>

server/embed/serve.go

@@ -234,7 +234,7 @@ func (sctx *serveCtx) registerGateway(opts []grpc.DialOption) (*gw.ServeMux, err
 	addr := sctx.addr
 	if network := sctx.network; network == "unix" {
 		// explicitly define unix network for gRPC socket support
-		addr = fmt.Sprintf("%s://%s", network, addr)
+		addr = fmt.Sprintf("%s:%s", network, addr)
 	}
 
 	opts = append(opts, grpc.WithDefaultCallOptions([]grpc.CallOption{