func (l *pingPacketList) Front() *pingPacket {
	return l.head
}
Front returns the first element of list l or nil.
package ping
type pingPacketElementMapper struct{}
func (pingPacketElementMapper) linkerFor(elem *pingPacket) *pingPacket { return elem }
type pingPacketList struct {
	head *pingPacket
	tail *pingPacket
}
func (l *pingPacketList) Reset() {
	l.head = nil
	l.tail = nil
}
func (l *pingPacketList) Empty() bool {
	return l.head == nil
}