[SCSI] qla4xxx: support iscsiadm session mgmt

Add scsi_transport_iscsi hooks in qla4xxx to support
iSCSI session management using iscsiadm.

This patch is based on discussion here
http://groups.google.com/group/open-iscsi/browse_thread/thread/e89fd888baf656a0#

Now users can use iscsiadm to do target discovery and do login/logout to
individual targets using the qla4xxx iSCSI class interface.

This patch leaves some dead code, but to make it easier to review
we are leaving and in the next patch we will remove that old code.

V2 - NOTE: Added code to avoid waiting for AEN during login/logout
in the driver, instead added a kernel to user event
to notify iscsid about login status. Because of this
iscsid will not get blocked.

Signed-off-by: Manish Rangankar <manish.rangankar@qlogic.com>
Signed-off-by: Lalit Chandivade <lalit.chandivade@qlogic.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>