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" <mst@redhat.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -28,7 +28,7 @@
 #include <linux/slab.h>
 #include <linux/cpu.h>
 
-static int napi_weight = 128;
+static int napi_weight = NAPI_POLL_WEIGHT;
 module_param(napi_weight, int, 0444);
 
 static bool csum = true, gso = true;