Linux 4.2: Pass namespace to sock_create_kern

Linux 4.2: Pass namespace to sock_create_kern

sock_create_kern gains an additional network namespace
argument.

Pass in the default system namesapce.

Reviewed-on: http://gerrit.openafs.org/11925
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Chas Williams <3chas3@gmail.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit e597b879677d023165298adadfb88db031883ff4)

Change-Id: I8e4341a6b4c33c5226b9307827932f577e08d5b2
Reviewed-on: http://gerrit.openafs.org/11948
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>