rx: always use/protect the xdr routines in the kernel

rx: always use/protect the xdr routines in the kernel

This clears up some warnings about duplicate symbols with Solaris 11
since the Solaris kernel already has these routines.  Since we never
use stock kernel version of the xdr routines perhaps we should always
use/protect our version of the symbols.

Change-Id: I4b5b4a691fb838093aff728469d17c28dccbaaea
Reviewed-on: http://gerrit.openafs.org/4252
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>