Linux: d_alias becomes d_u.d_alias

Linux: d_alias becomes d_u.d_alias

The fields in struct dentry are re-arranged so that d_alias
shares space wth d_rcu inside the d_u union.  Some references
need to change from d_alias to d_u.d_alias.

The kernel change was introduced for 3.19 but was also backported
to the 3.18 stable series in 3.18.1, so this commit is required
for 3.19 and current 3.18 kernels.

Reviewed-on: http://gerrit.openafs.org/11642
Reviewed-by: Anders Kaseorg <andersk@mit.edu>
Reviewed-by: Michael Laß <lass@mail.uni-paderborn.de>
Reviewed-by: Daria Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit d6f29679098aff171e69511823b340ccf28e5c31)

Change-Id: Ifb6199aa7fa922e64540d9fad1d2d79facbb9761
Reviewed-on: http://gerrit.openafs.org/11659
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Daria Brashear <shadow@your-file-system.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>