buildroot

hostapd: select driver support

Add support for the wired driver. Add configuration options to select
which drivers to build. Select DRIVER_NONE if no other drivers enabled
(this may be the case when building hostapd as a standalone RADIUS
server).

Update makefile logic and apply wireless-specific options only if at
least one wireless driver enabled. Otherwise, an attempt to build a
wired-only or RADIUS-only hostapd will fail.

Signed-off-by: Alexander Mukhin <alexander.i.mukhin@gmail.com>
Reviewed-by: Sam Voss <sam.voss@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>