[SCSI] qla4xxx: Clear DDB map index on the basis of AEN.

Unable to login to session if login-logout issued consecutively for
multiple sessions. Solution is to clear idx in DDB map on the basis
of no-active connection asynchronous event (AEN).

JIRA Key: UPSISCSI-135

Signed-off-by: Manish Rangankar <manish.rangankar@qlogic.com>
Signed-off-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>