docs: Refer to dafs binaries by their real names

docs: Refer to dafs binaries by their real names

(Most of) the dafs binaries are called da(something). Update the
example in the dafileserver documentation so that we call the binaries
by the names that they are actually installed with on the system.

Reviewed-on: http://gerrit.openafs.org/5654
Tested-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit c37a14697df291f641b4fa5a32826054d92210b0)

Change-Id: I001a0e2c94a7c52d91b2ebf257d097ce7400eb3a
Reviewed-on: http://gerrit.openafs.org/5703
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: Derrick Brashear <shadow@dementix.org>