[SCSI] iscsi class: Add new NETLINK_ISCSI messages for cnic/bnx2i driver.

Add ISCSI_NETLINK messages for iSCSI NICs to get information such as
path from userspace.  Original iscsid messages are now always sent as
multicast to group 1.  The new messages are sent to group 2.

The multicast changes were made by Mike Christie.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>