LINUX: Avoid multiple d_invalidate loops

Currently, in afs_linux_lookup, we put an artificial limit on how many
times we loop through all dentry aliases, trying ti d_invalidate all
of them. Instead of using an arbitrary limit, we can just go through
all of them once, by using d_prune_aliases. This should be faster, and
removes some of the logic required here.

Note that this does remove our check for DCACHE_DISCONNECTED in each
alias' d_flags.  This should not be a problem, since we will still use
any remaining DCACHE_DISCONNECTED dentry via d_splice_alias if one
still exists.

Reviewed-on: http://gerrit.openafs.org/8751
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 370aaaeafa43f804b0a5286d92b4ec5f1ccb62be)

Change-Id: I1aa70afe8268852c676f241e0189bc010ad757aa
Reviewed-on: http://gerrit.openafs.org/9288
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Tested-by: BuildBot <buildbot@rampaginggeek.com>