io_uring: Introduce IORING_OP_LISTEN

IORING_OP_LISTEN provides the semantic of listen(2) via io_uring.  While
this is an essentially synchronous system call, the main point is to
enable a network path to execute fully with io_uring registered and
descriptorless files.

Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Link: https://lore.kernel.org/r/20240614163047.31581-4-krisman@suse.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>