io_uring: add IORING_ACCEPT_MULTISHOT for accept

add an accept_flag IORING_ACCEPT_MULTISHOT for accept, which is to
support multishot.
Signed-off-by: Hao Xu <howeyxu@tencent.com>
Link: https://lore.kernel.org/r/20220514142046.58072-2-haoxu.linux@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

include/uapi/linux/io_uring.h

@@ -232,6 +232,11 @@ enum {
  */
 #define IORING_RECVSEND_POLL_FIRST	(1U << 0)
 
+/*
+ * accept flags stored in sqe->ioprio
+ */
+#define IORING_ACCEPT_MULTISHOT	(1U << 0)
+
 /*
  * IO completion data structure (Completion Queue Entry)
  */