Merge branch 'tcp-rfc-6056'

Eric Dumazet says:

====================
tcp: RFC 6056 induced changes

This is based on a report from David Dworken.

First patch implements RFC 6056 3.3.4 proposal.

Second patch is adding a little bit of noise to make
attacker life a bit harder.
===================

Signed-off-by: David S. Miller <davem@davemloft.net>