hostapd: enable compilation of OCV and add build feature discovery

hostapd: enable compilation of OCV and add build feature discovery

Operating Channel Validation (OCV) is a security feature designed to
prevent person-in-the-middle multi-channel attacks. Compile the -basic and
-full variants of hostapd with this feature, and enable discovery of this
feature for future luci integration. OCV can be configured by setting ocv
equal to one of the following values in the wireless config:

0 = disabled (hostapd/wpa_supplicant default)
1 = enabled
2 = enabled in workaround mode - Allow STA that claims OCV capability to
    connect even if the STA doesn't send OCI or negotiate PMF.

Signed-off-by: Michael Yartys <michael.yartys@protonmail.com>