namei: Set inconsistent linktable linkCount to 0

Currently, if we detect an inconsistent linktable filename (where the
filename indicates it's for a different volume than the directory path
indicates), we don't set the linkCount for the inode info. This means
that our caller will get random garbage for the linkCount.

In many cases this value is ignored, but for the salvager, if this is
the only linktable file we find, we treat it as the linktable we
should be using. Thus, if linkCount contains undefined data, we might
try to INC or DEC the linktable a bunch of times, depending on what
random stack garbage the linkCount is filled with.

The salvager shouldn't be INC/DEC'ing these linktables according to
the their linkCount anyway, but in the meantime, at least ensure that
this doesn't contain stack garbage, so we ensure that we won't try to
INC or DEC this thousands or millions of times.

Change-Id: Ib5e7f45d5739878434cbe57b6f2ab532f002e5b8
Reviewed-on: http://gerrit.openafs.org/10320
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>