code: func newMruNonceMap(limit uint) *mruNonceMap {
  	m := mruNonceMap{
  		nonceMap:  make(map[uint64]*list.Element),
  		nonceList: list.New(),
  		limit:     limit,
  	}
  	return &m
  }
docs: // newMruNonceMap returns a new nonce map that is limited to the number of
  // entries specified by limit.  When the number of entries exceeds the limit,
  // the oldest (least recently used) entry will be removed to make room for the
  // new entry.