[SCSI] qla4xxx: update function qla4xxx_isr_decode_mailbox()

- Added MBOX_ASTS_DUPLICATE_IP AEN handling.
- Update MBOX_AEN_REG_COUNT to 8 so that driver will save status
  of all mbox registers in aen_q

Signed-off-by: Prasanna Mumbai <prasanna.mumbai@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>