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)
}
TOS returns the type-of-service field value for outgoing packets.
package ipv4