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_erl0.c

@@ -746,13 +746,12 @@ int iscsit_check_post_dataout(
 		if (!conn->sess->sess_ops->ErrorRecoveryLevel) {
 			pr_err("Unable to recover from DataOUT CRC"
 				" failure while ERL=0, closing session.\n");
-			iscsit_add_reject_from_cmd(ISCSI_REASON_DATA_DIGEST_ERROR,
-					1, 0, buf, cmd);
+			iscsit_reject_cmd(cmd, ISCSI_REASON_DATA_DIGEST_ERROR,
+					  buf);
 			return DATAOUT_CANNOT_RECOVER;
 		}
 
-		iscsit_add_reject_from_cmd(ISCSI_REASON_DATA_DIGEST_ERROR,
-				0, 0, buf, cmd);
+		iscsit_reject_cmd(cmd, ISCSI_REASON_DATA_DIGEST_ERROR, buf);
 		return iscsit_dataout_post_crc_failed(cmd, buf);
 	}
 }