scsi: iscsi_tcp: Fix shost can_queue initialization

We are setting the shost's can_queue after we add the host which is too
late, because the SCSI midlayer will have allocated the tag set based on
the can_queue value at that time. This patch has us use the
iscsi_host_get_max_scsi_cmds() helper to figure out the number of SCSI
cmds.

It also fixes up the template can_queue so it reflects the max SCSI cmds we
can support like how other drivers work.

Link: https://lore.kernel.org/r/20210207044608.27585-7-michael.christie@oracle.com


Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>