Build on linux 2.4 again

Build on linux 2.4 again

Add missing conditional to fix building on
linux 2.4.

FIXES 125120

Reviewed-on: http://gerrit.openafs.org/http://gerrit.openafs.org/148
Tested-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Tested-by: Russ Allbery <rra@stanford.edu>
Reviewed-by: Russ Allbery <rra@stanford.edu>
(cherry picked from commit f6e46babd8e3a0d51d31ae381748516330f5b84d)
Reviewed-on: http://gerrit.openafs.org/386
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>