libafsauthent: export additional xdr_ functions

libafsauthent: export additional xdr_ functions

Formally, we need to use xdr_free to deallocate storage for RPC output
variables, in case the XDR stack uses a different allocator than the
standard application allocator.  Some types have non-autogenerated
wrappers exposed already (e.g., token_FreeSet()), but for a handful of
the base ptint types we need to expose the xdr routines in order for a
safe way to deallocate their storage to be available.

Change-Id: Iaac349cfaa1a07d5908a88e4c230874c6301471a
Reviewed-on: https://gerrit.openafs.org/13131
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>