iscsi-target: Remove SCF_SE_LUN_CMD flag abuses

This patch removes a number of SCF_SE_LUN_CMD flag abuses within iscsi-target
code to determine when iscsit_release_cmd() or transport_generic_free_cmd()
should be called while releasing an individual iscsi_cmd descriptor.

In the place of SCF_SE_LUN_CMD checks, this patch converts existing code to
use a new iscsit_free_cmd() that inspects iscsi_cmd->iscsi_opcode types to
determine which of the above functions should be invoked.  It also removes the
now unnecessary special case checking in iscsit_release_commands_from_conn().

(hch: Use iscsit_free_cmd instead of open-coded alternative)

Reported-by: Christoph Hellwig <hch@lst.de>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/target/iscsi/iscsi_target_util.h b/drivers/target/iscsi/iscsi_target_util.h
index 2cd49d6..835bf7d 100644
--- a/drivers/target/iscsi/iscsi_target_util.h
+++ b/drivers/target/iscsi/iscsi_target_util.h
@@ -30,6 +30,7 @@
 extern void iscsit_remove_cmd_from_tx_queues(struct iscsi_cmd *, struct iscsi_conn *);
 extern void iscsit_free_queue_reqs_for_conn(struct iscsi_conn *);
 extern void iscsit_release_cmd(struct iscsi_cmd *);
+extern void iscsit_free_cmd(struct iscsi_cmd *);
 extern int iscsit_check_session_usage_count(struct iscsi_session *);
 extern void iscsit_dec_session_usage_count(struct iscsi_session *);
 extern void iscsit_inc_session_usage_count(struct iscsi_session *);