virtio_net: use default napi weight by default

virtio_net: use default napi weight by default

Since commit 82dc3c63c692b1e1d5937 ("net: introduce NAPI_POLL_WEIGHT")
we warn drivers when they use napi weight higher than NAPI_POLL_WEIGHT,
but virtio_net still uses 128 by default. This patch makes its default
value to NAPI_POLL_WEIGHT.

Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: David S. Miller <[email protected]>
Signed-off-by: Cong Wang <[email protected]>
Signed-off-by: David S. Miller <[email protected]>