iSNS: Event registry and notification

[Raghavendra Rao <jp.raghavendra@sun.com>]

In reviewing -02 spec of iSNS,  the event registration and notification
need
more work to live up to the promise (and requirement of Naming and
discovery spec) of being lightweight. Right now, it defines catch-all
and receive-all events.

To start with, an iSCSI initiator MUST be able to register

 a) for state changes of specific/interested iSCSI targets.

 b) for addition of iSCSI targets that provide Login access control
    to this iSCSI initiator

Along similar lines, it would also help to provide an iSCSI target the
ability to register for an event when an iSCSI initiator is
added/removed
to the login control list of this iSCSI target. An iSCSI target, upon
receiving such a notification, can then simply download the updated
list of allowed iSCSI initiators.

Such types of notifications help reduce notification storms by
 - Helping a small iSCSI initiator client receive and process
   absolutely required notification (Note that totally turning
   off notification is a BAD idea)

 - Reducing needless traffic.

-JP