Add FILS support to hostapd

Hi everyone!

I've recently been interested in enabling FILS support in OpenWRT and as recently the patch disabling FILS has been removed I thought it was the perfect opportunity to enable it.

I have little knowledge of scripting so my script may be far from perfect so anyone is welcome to help!
If you think I should make a pull request to work there on this feature let me know.

As for the results of the current work developed it is partially working, in the sense that, when enabled with:

option 80211ai '1'

The AP comes up and in the beacons I can see the FILS capability, the RSN authentication and the FILS Indication tag, the Windows laptops can connect to the wifi but the android phones can't... I believe this is because the windows devices don't support FILS so they use the other authentication methods available (?).
Once I can I'll do a capture with a wifi monitor to see what is happening.

In the meantime here is my repo:

Thanks!