CVE-2019-10638

According to Amit Klein and Benny Pinkas, IP ID generation is too weak
and might be used by attackers.

Even with recent net_hash_mix() fix (netns: provide pure entropy for net_hash_mix())
having 64bit key and Jenkins hash is risky.

It is time to switch to siphash and its 128bit keys.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Amit Klein <aksecurity@gmail.com>
Reported-by: Benny Pinkas <benny@pinkas.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
(backported from commit df453700)
[ Connor Kuehl: Adjusted patch to communicate the id return value
  through the skbuf as the function signature for ipv6_proxy_select_ident
  is still void (whereas the patch context expects it to return a
  value). This function signature change doesn't happen until upstream
  commit: 0c19f846 "net: accept UFO datagrams from tuntap and packet" ]
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Acked-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>