io_uring: check reserved fields for send/sendmsg

io_uring: check reserved fields for send/sendmsg

BugLink: https://bugs.launchpad.net/bugs/1978234
[ Upstream commit 588faa1ea5eecb351100ee5d187b9be99210f70d ]

We should check unused fields for non-zero and -EINVAL if they are set,
making it consistent with other opcodes.

Fixes: 0fa03c624d8f ("io_uring: add support for sendmsg()")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>