MFC r337775:

MFC r337775:
  Improve hashing of IPv4 fragments.

  Currently, IPv4 fragments are hashed into buckets based on a 32-bit
  key which is calculated by (src_ip ^ ip_id) and combined with a random
  seed. However, because an attacker can control the values of src_ip
  and ip_id, it is possible to construct an attack which causes very
  deep chains to form in a given bucket.

  To ensure more uniform distribution (and lower predictability for
  an attacker), calculate the hash based on a key which includes all
  the fields we use to identify a reassembly queue (dst_ip, src_ip,
  ip_id, and the ip protocol) as well as a random seed.

Security:	FreeBSD-SA-18:10.ip
Security:	CVE-2018-6923