[eapol] Delay EAPoL-Start while waiting for EAP to complete

[eapol] Delay EAPoL-Start while waiting for EAP to complete

EAP exchanges may take a long time to reach a final status, especially
when relying upon MAC Authentication Bypass (MAB).  Our current
behaviour of sending EAPoL-Start every few seconds until a final
status is obtained can prevent these exchanges from ever completing.

Fix by redefining the EAP supplicant state to allow EAPoL-Start to be
suppressed: either temporarily (while waiting for a full EAP exchange
to complete, in which case we need to eventually resend EAPoL-Start if
the final Success or Failure packet is lost), or permanently (while
waiting for the potentially very long MAC Authentication Bypass
timeout period).

Signed-off-by: Michael Brown <mcb30@ipxe.org>