func (c *dgramOpt) SetMulticastInterface(ifi *net.Interface) error {
	if !c.ok() {
		return syscall.EINVAL
	}
	so, ok := sockOpts[ssoMulticastInterface]
	if !ok {
		return errOpNoSupport
	}
	return so.setMulticastInterface(c.Conn, ifi)
}
SetMulticastInterface sets the default interface for future
multicast packet transmissions.
package ipv4
import (
	"net"
	"syscall"
	"golang.org/x/net/bpf"
)
func (c *dgramOpt) MulticastTTL() (int, error) {
	if !c.ok() {
		return 0, syscall.EINVAL
	}
	so, ok := sockOpts[ssoMulticastTTL]
	if !ok {
		return 0, errOpNoSupport
	}
	return so.GetInt(c.Conn)
}
func (c *dgramOpt) SetMulticastTTL(ttl int) error {
	if !c.ok() {
		return syscall.EINVAL
	}
	so, ok := sockOpts[ssoMulticastTTL]
	if !ok {
		return errOpNoSupport
	}
	return so.SetInt(c.Conn, ttl)
}
func (c *dgramOpt) MulticastInterface() (*net.Interface, error) {
	if !c.ok() {
		return nil, syscall.EINVAL
	}
	so, ok := sockOpts[ssoMulticastInterface]
	if !ok {
		return nil, errOpNoSupport
	}
	return so.getMulticastInterface(c.Conn)
}