kauth: Don't overflow cellinfo hostAddrs array

The hostaddrs array has MAXHOSTSPERCELL (8) available elements.
The ubik connections list has MAXSERVERS (20) elements - when copying
from the ubik list into the cellinfo hostaddrs list, be careful not
to overflow it.

Caught by coverity (#985577)

Reviewed-on: http://gerrit.openafs.org/9323
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 30e25c74376dd8aa24018116015e57c47c1dfaf9)

Change-Id: I6bf03fada98cf6f5442a7d6a1e52e18cc91aad59
Reviewed-on: http://gerrit.openafs.org/9375
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Paul Smeddle <paul.smeddle@gmail.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>