hostapd: add wpa_disable_eapol_key_retries option

Commit 2127425434046ae2b9f02fdbbdd37cac447af19c introduced an AP-side
workaround for key reinstallation attacks. This option can be used to
mitigate KRACK on the station side, in case those stations cannot be
updated. Since many devices are out there will not receive an update
anytime soon (if at all), it makes sense to include this workaround.

Unfortunately this can cause interoperability issues and reduced
robustness of key negotiation, so disable the workaround by default, and
add an option to allow the user to enable it if he deems necessary.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>