Fix build when WITHOUT_WPA_SUPPLICANT_EAPOL option used.

The build failure was discoved by Michael Dexter's recent Build Options
Survey run, at https://callfortesting.org/results/bos-2020-01-16/\
WITHOUT_WPA_SUPPLICANT_EAPOL-small.txt.

Reported by: Michael Dexter <editor@callfortesting.org> via emaste
MFC after: 2 weeks