scsi: blkcg: Add app identifier support for blkcg

scsi: blkcg: Add app identifier support for blkcg

Add a unique application identifier (i.e fc_app_id member) in blkcg. This
allows identification of traffic belonging to an specific both on the host
and in the fabric infrastructure. As an example, this allows the storage
stack to uniquely identify traffic belong to particular virtual machine.

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Himanshu Madhani <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Muneendra Kumar <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>