iscsi-target: Fix iscsit_add_reject* usage for iser

This patch changes iscsit_add_reject() + iscsit_add_reject_from_cmd()
usage to not sleep on iscsi_cmd->reject_comp to address a free-after-use
usage bug in v3.10 with iser-target code.

It saves ->reject_reason for use within iscsit_build_reject() so the
correct value for both transport cases.  It also drops the legacy
fail_conn parameter usage throughput iscsi-target code and adds
two iscsit_add_reject_cmd() and iscsit_reject_cmd helper functions,
along with various small cleanups.

(v2: Re-enable target_put_sess_cmd() to be called from
     iscsit_add_reject_from_cmd() for rejects invoked after
     target_get_sess_cmd() has been called)

Cc: Or Gerlitz <ogerlitz@mellanox.com>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: stable@vger.kernel.org  # 3.10+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.h

@@ -15,7 +15,7 @@ extern struct iscsi_np *iscsit_add_np(struct __kernel_sockaddr_storage *,
 extern int iscsit_reset_np_thread(struct iscsi_np *, struct iscsi_tpg_np *,
 				struct iscsi_portal_group *);
 extern int iscsit_del_np(struct iscsi_np *);
-extern int iscsit_add_reject_from_cmd(u8, int, int, unsigned char *, struct iscsi_cmd *);
+extern int iscsit_reject_cmd(struct iscsi_cmd *cmd, u8, unsigned char *);
 extern void iscsit_set_unsoliticed_dataout(struct iscsi_cmd *);
 extern int iscsit_logout_closesession(struct iscsi_cmd *, struct iscsi_conn *);
 extern int iscsit_logout_closeconnection(struct iscsi_cmd *, struct iscsi_conn *);