Prevent hostapd units from being started if there’s no config provided

See: https://bugs.debian.org/1028088 and infrastructure/apertis-issues#388 (closed)

This fix is backported from https://salsa.debian.org/debian/wpa/-/commit/d204ceb5a2dc33db888eb55b5fee542a1005e69c

Signed-off-by: Dylan Aïssi dylan.aissi@collabora.com