nbd: handle interrupted sendmsg with a sndtimeo set

nbd: handle interrupted sendmsg with a sndtimeo set

If you do not set sk_sndtimeo you will get -ERESTARTSYS if there is a
pending signal when you enter sendmsg, which we handle properly.
However if you set a timeout for your commands we'll set sk_sndtimeo to
that timeout, which means that sendmsg will start returning -EINTR
instead of -ERESTARTSYS.  Fix this by checking either cases and doing
the correct thing.

Cc: [email protected]
Fixes: dc88e34d69d8 ("nbd: set sk->sk_sndtimeo for our sockets")
Reported-and-tested-by: Daniel Xu <[email protected]>
Signed-off-by: Josef Bacik <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>