target/iscsi: Refactor target_tx_thread immediate+response queue loops

Immediate queue:

Consolidate down to one switch statement by moving send_tx_data and stuff
from second switch into the first switch, or the functions the first switch
calls.

Response queue:

Do not lock istate_lock except directly around i_state modifications.

Put entire ISTATE_SEND_DATAIN path within first switch statement, in prep
for further refactoring.

All other cases set use_misc = 1 and will not be using sendpage, so just
use send_tx_data for these and set use_misc param to 1.

map_sg, sent_status, use_misc, and se_cmd vars no longer needed.

Then put immediate and response handling in separate functions in order
to get iscsi_target_tx_thread down to where it fits on a page.
Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.h

@@ -18,7 +18,6 @@ extern int iscsit_logout_closesession(struct iscsi_cmd *, struct iscsi_conn *);
 extern int iscsit_logout_closeconnection(struct iscsi_cmd *, struct iscsi_conn *);
 extern int iscsit_logout_removeconnforrecovery(struct iscsi_cmd *, struct iscsi_conn *);
 extern int iscsit_send_async_msg(struct iscsi_conn *, u16, u8, u8);
-extern int iscsit_send_r2t(struct iscsi_cmd *, struct iscsi_conn *);
 extern int iscsit_build_r2ts_for_cmd(struct iscsi_cmd *, struct iscsi_conn *, int);
 extern void iscsit_thread_get_cpumask(struct iscsi_conn *);
 extern int iscsi_target_tx_thread(void *);