This patch fixes the netdev document description typo in qemu-option.hx.

Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20200727045925.29375-1-tianjia.zhang@linux.alibaba.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>