[RFC 1/2 RESEND] hostapd: add AFC client support

[Arnon Meydav]

> Introduce Automated Frequency Coordination (AFC) support for UNII-5 and
> UNII-7 6GHz bands.

I discussed the afc client implementation with some colleagues who have been working on afc at Maxlinear.

Here are some of our inputs:
1. In general, we like this concept of adding the afc client to hostapd, as it reduces the complexity of needing to sync hostapd with an external afc application, and the addition of the eirp and psd power to the channel data is an important enhancement.

2. We have some comments that are best to be addressed before merging:
2.a. The code assumes JSON is returning int, not float, whereas some afc servers return the power level in float.
2.b. Missing a curl option, VERIFYSTATUS, which is needed in order to pass certification.
2.c. max_eirp_psd and  max_eirp_power are stored and used as whole values, instead of units of 0.5 dBm and 0.5 dBm/MHz, like they are in the Transmitted Power Envelope IEs .
It is important to store in half units for easier extension and more accurate usage.

Best regards,
Arnon