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)

Change-Id: Ie51cb939a6e3381a285787ad125342ca7a9e7cbb
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>