func (c *genericOpt) SetTOS(tos int) error {
	if !c.ok() {
		return errInvalidConn
	}
	so, ok := sockOpts[ssoTOS]
	if !ok {
		return errOpNoSupport
	}
	return so.SetInt(c.Conn, tos)
}
SetTOS sets the type-of-service field value for future outgoing
packets.
package ipv4
func (c *genericOpt) TOS() (int, error) {
	if !c.ok() {
		return 0, errInvalidConn
	}
	so, ok := sockOpts[ssoTOS]
	if !ok {
		return 0, errOpNoSupport
	}
	return so.GetInt(c.Conn)
}