virtio_net: fix missing lock protection on control_buf access

Refactored the handling of control_buf to be within the cvq_lock
critical section, mitigating race conditions between reading device
responses and new command submissions.

Fixes: 6f45ab3e ("virtio_net: Add a lock for the command VQ.")
Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Hariprasad Kelam <hkelam@marvell.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240530034143.19579-1-hengqi@linux.alibaba.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>