func (b NDPRouterAdvert) ReachableTime() time.Duration {
	return time.Millisecond * time.Duration(binary.BigEndian.Uint32(b[ndpRAReachableTimeOffset:]))
}
ReachableTime returns the time that a node assumes a neighbor is reachable
after having received a reachability confirmation. A value of 0 means
that it is unspecified by the source of the Router Advertisement message.
package header
import (
	"encoding/binary"
	"time"
)
type NDPRouterAdvert []byte
const (
	NDPRAMinimumSize = 12
	ndpRACurrHopLimitOffset = 0
	ndpRAFlagsOffset = 1
	ndpRAManagedAddrConfFlagMask = (1 << 7)
	ndpRAOtherConfFlagMask = (1 << 6)
	ndpRARouterLifetimeOffset = 2
	ndpRAReachableTimeOffset = 4
	ndpRARetransTimerOffset = 8
	ndpRAOptionsOffset = 12
)
func (b NDPRouterAdvert) CurrHopLimit() uint8 {
	return b[ndpRACurrHopLimitOffset]
}
func (b NDPRouterAdvert) ManagedAddrConfFlag() bool {
	return b[ndpRAFlagsOffset]&ndpRAManagedAddrConfFlagMask != 0
}
func (b NDPRouterAdvert) OtherConfFlag() bool {
	return b[ndpRAFlagsOffset]&ndpRAOtherConfFlagMask != 0
}
func (b NDPRouterAdvert) RouterLifetime() time.Duration {
	return time.Second * time.Duration(binary.BigEndian.Uint16(b[ndpRARouterLifetimeOffset:]))
}