wext: Re-add support for SIGNAL_POLL and DRIVER

Both of these are still used by JB, and wext wifi drivers have some
weird behaviors without it (like a reported poor connection 100% of
the time)

Change-Id: I15339dbea4e15831465e2bb52b11675cb20dc34c
Fix regression in LEAP

Commit 458cb3019108b6cb8c0c1cab94ae6ebf244eda27 broke LEAP since it
rejects EAP-Success packet that is used within LEAP and this frame does
not have a payload. Fix LEAP by relaxing the generic EAP packet
validation if LEAP has been negotiated.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>