io_uring: Avoid anonymous enums in io_uring uapi

io_uring: Avoid anonymous enums in io_uring uapi

While valid C, anonymous enums confuse Cython (Python to C translator),
as reported by Ritesh (YoSTEALTH) [1] .  Since people rely on it when
building against liburing and we want to keep this header in sync with
the library version, let's name the existing enums in the uapi header.

[1] https://github.com/cython/cython/issues/3240

Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Link: https://lore.kernel.org/r/20240328210935.25640-1-krisman@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>