vfs_io_uring: avoid stack recursion of vfs_io_uring_queue_run()

vfs_io_uring: avoid stack recursion of vfs_io_uring_queue_run()

Instead we remember if recursion was triggered and jump to
the start of the function again from the end.

This should make it safe to be called from the completion_fn().

This is hideously complex stuff, so document the hell
out of it.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14361

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>