code: func (fi *FastIntegerHashMap) rebuild() {
  	packets := make(packets, roundUp(uint64(len(fi.packets))+1))
  	for _, packet := range fi.packets {
  		if packet == nil {
  			continue
  		}
  
  		packets.set(packet)
  	}
  	fi.packets = packets
  }
docs: // rebuild is an expensive operation which requires us to iterate
  // over the current bucket and rehash the keys for insertion into
  // the new bucket.  The new bucket is twice as large as the old
  // bucket by default.