add path option support for grpc

dialer/grpc/metadata.go

@@ -8,16 +8,19 @@ import (
 type metadata struct {
 	insecure bool
 	host     string
+	path     string
 }
 
 func (d *grpcDialer) parseMetadata(md mdata.Metadata) (err error) {
 	const (
 		insecure = "grpcInsecure"
 		host     = "host"
+		path     = "path"
 	)
 
 	d.md.insecure = mdx.GetBool(md, insecure)
 	d.md.host = mdx.GetString(md, host)
+	d.md.path = mdx.GetString(md, path)
 
 	return
 }