Export {Get,Set}ServiceSpecific from liboafs_rx.la

Export {Get,Set}ServiceSpecific from liboafs_rx.la

rxgk will use service-specific data.

Change-Id: Id9e2d4b9920e771e1583b9362e61de6216c246b4
Reviewed-on: https://gerrit.openafs.org/10589
Reviewed-by: Daria Phoebe Brashear <dariaphoebe@auristor.com>
Reviewed-by: Chas Williams <3chas3@gmail.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>