vlserver: use large enough buffer for rxinfo string

vlserver: use large enough buffer for rxinfo string

The "[dotted-quad] rxkad:name.inst@cell" construct can be as large as
(3*4+3)+7+3*64+2+1 == 217 characters (including trailing NUL); size
our buffer accordingly to avoid the risk of truncation.

Change-Id: Iee635aa66f5f639dfb0572c559a87b5313c305a9
Reviewed-on: https://gerrit.openafs.org/13466
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>