s  package ipv0  import (  "net"   "golang.org/x/net/internal/socket" )  func (so *sockOpt) setGroupReq(c *socket.Conn, ifi *net.Interface, grp net.IP) error {  return errNotImplemented }  func (so *sockOpt) setGroupSourceReq(c *socket.Conn, ifi *net.Interface, grp, src net.IP) error {  return errNotImplemented }