cifs: add new cifsiod_wq workqueue

...and convert existing cifs users of system_nrt_wq to use that instead.

Also, make it freezable, and set WQ_MEM_RECLAIM since we use it to
deal with write reply handling.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>

fs/cifs/misc.c

@@ -595,7 +595,7 @@ is_valid_oplock_break(char *buffer, struct TCP_Server_Info *srv)
 
 				cifs_set_oplock_level(pCifsInode,
 					pSMB->OplockLevel ? OPLOCK_READ : 0);
-				queue_work(system_nrt_wq,
+				queue_work(cifsiod_wq,
 					   &netfile->oplock_break);
 				netfile->oplock_break_cancelled = false;