virtio-net: Reduce debug name field size to 16 bytes

virtio queue index can be maximum of 65535. 16 bytes are enough to store
the vq name with the existing string prefix.

With this change, send queue struct saves 24 bytes and receive
queue saves whole cache line worth 64 bytes per structure
due to saving in alignment bytes.

Pahole results before:

pahole -s drivers/net/virtio_net.o | \
    grep -e "send_queue" -e "receive_queue"
send_queue      1112    0
receive_queue   1280    1

Pahole results after:
pahole -s drivers/net/virtio_net.o | \
    grep -e "send_queue" -e "receive_queue"
send_queue      1088    0
receive_queue   1216    1

Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>