iscsi-target: Prepare login code for multi-plexing support

This patch prepares the iscsi-target login code for multi-plexing
support.  This includes:

 - Adding iscsi_tpg_np->tpg_np_kref + iscsit_login_kref_put() for
   handling callback of iscsi_tpg_np->tpg_np_comp
 - Adding kref_put() in iscsit_deaccess_np()
 - Adding kref_put() and wait_for_completion() in
   iscsit_reset_np_thread()
 - Refactor login failure path release logic into
   iscsi_target_login_sess_out()
 - Update __iscsi_target_login_thread() to handle
   iscsi_post_login_handler() asynchronous completion
 - Add shutdown parameter for iscsit_clear_tpg_np_login_thread*()

v3 changes:
 - Convert iscsi_portal_group->np_login_lock to ->np_login_sem
 - Add LOGIN_FLAGS definitions

v2 changes:
 - Remove duplicate call to iscsi_post_login_handler() in
   __iscsi_target_login_thread()
 - Drop unused iscsi_np->np_login_tpg

Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.h

@@ -7,13 +7,15 @@ extern void iscsit_put_tiqn_for_login(struct iscsi_tiqn *);
 extern struct iscsi_tiqn *iscsit_add_tiqn(unsigned char *);
 extern void iscsit_del_tiqn(struct iscsi_tiqn *);
 extern int iscsit_access_np(struct iscsi_np *, struct iscsi_portal_group *);
-extern int iscsit_deaccess_np(struct iscsi_np *, struct iscsi_portal_group *);
+extern void iscsit_login_kref_put(struct kref *);
+extern int iscsit_deaccess_np(struct iscsi_np *, struct iscsi_portal_group *,
+				struct iscsi_tpg_np *);
 extern bool iscsit_check_np_match(struct __kernel_sockaddr_storage *,
 				struct iscsi_np *, int);
 extern struct iscsi_np *iscsit_add_np(struct __kernel_sockaddr_storage *,
 				char *, int);
 extern int iscsit_reset_np_thread(struct iscsi_np *, struct iscsi_tpg_np *,
-				struct iscsi_portal_group *);
+				struct iscsi_portal_group *, bool);
 extern int iscsit_del_np(struct iscsi_np *);
 extern int iscsit_reject_cmd(struct iscsi_cmd *cmd, u8, unsigned char *);
 extern void iscsit_set_unsoliticed_dataout(struct iscsi_cmd *);