rnbd-srv: Zero the rsp buffer before using it

rnbd-srv: Zero the rsp buffer before using it

Before using the data buffer to send back the response message, zero it
completely. This prevents any stray bytes to be picked up by the client
side when there the message is exchanged between different protocol
versions.

Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Grzegorz Prajsner <grzegorz.prajsner@ionos.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>