ibmvscsis: Use tpgt passed in by user

ibmvscsis always returned 0 for the tpg/tag, since it did not
parse the value passed in by the user.

When functions like ALUA members exports the value, it will
be incorrect because targetcli/rtslib starts the tpg numbering
at 1.
Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c

@@ -3914,8 +3914,16 @@ static struct se_portal_group *ibmvscsis_make_tpg(struct se_wwn *wwn,
 {
 	struct ibmvscsis_tport *tport =
 		container_of(wwn, struct ibmvscsis_tport, tport_wwn);
+	u16 tpgt;
 	int rc;
 
+	if (strstr(name, "tpgt_") != name)
+		return ERR_PTR(-EINVAL);
+	rc = kstrtou16(name + 5, 0, &tpgt);
+	if (rc)
+		return ERR_PTR(rc);
+	tport->tport_tpgt = tpgt;
+
 	tport->releasing = false;
 
 	rc = core_tpg_register(&tport->tport_wwn, &tport->se_tpg,