Merge branch 'tcp-keepalive-namespaceify'

Nikolay Borisov says:

====================
Namespaceify tcp keepalive machinery

The following patch series enables the tcp keepalive mechanism
to be configured per net namespace. This is especially useful
if you have multiple containers hosted on one node and one of
them is under DoS-  in such situations one thing which could
be done is to configure the tcp keepalive settings such that
connections for that particular container are being reset
faster.

Another scenario where not being able to control those knob
comes per container is problematic is occurs the value of
net.netfilter.nf_conntrack_tcp_timeout_established is set
below the keepalive interval, in such situations the server won't
send an RST packet resulting in applications not trying to
reconnect and stale connection waiting. Changing the global
keepalive value is a possible solution but it might interfere
with other containers.

The three patches gradually convert each of the affected knobs
to be per netns. I thought it would be easier for review than
put everything in one patch. If people deem it more appropriate
to squash everything in one patch (maybe after review) I'd
be more than happy to do it.

The patches have been compile-tested on 4.4 and functionally
tested on 3.12 and they work as expected.

These are based off 4.4-rc8
====================

Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>