Fix fallback from failed PMKSA caching into full EAP authentication

Fix fallback from failed PMKSA caching into full EAP authentication

Commit 83935317a78fb4157eb6e5134527b9311dbf7b8c added forced
disconnection in case of 4-way handshake failures. However, it should
not have changed the case where the supplicant is requesting fallback
to full EAP authentication if the PMKID in EAPOL-Key message 1/4 is
not know. This case needs to send an EAPOL-Start frame instead of
EAPOL-Key message 2/4.

This works around a problem with APs that try to force PMKSA caching
even when the client does not include PMKID in (re)association request
frame to request it. [Bug 355]