virtio: Skip RX checksum validation if not requested
virtio: Skip RX checksum validation if not requested

Don't validate the checksum of incoming packets unless the
VIRTIO_NET_F_CSUM feature is negotiated.

This saves work with guests that do not care about the checksum L4
status e.g. DPDK-based routers.

heryii/snabb,dpino/snabb,SnabbCo/snabbswitch,justincormack/snabbswitch,SnabbCo/snabbswitch,wingo/snabbswitch,pirate/snabbswitch,dpino/snabb,Igalia/snabb,lukego/snabb,hb9cwp/snabbswitch,Igalia/snabbswitch,heryii/snabb,eugeneia/snabb,wingo/snabbswitch,heryii/snabb,andywingo/snabbswitch,eugeneia/snabb,dpino/snabbswitch,plajjan/snabbswitch,hb9cwp/snabbswitch,snabbnfv-goodies/snabbswitch,Igalia/snabbswitch,snabbnfv-goodies/snabbswitch,alexandergall/snabbswitch,eugeneia/snabbswitch,Igalia/snabb,plajjan/snabbswitch,lukego/snabbswitch,alexandergall/snabbswitch,andywingo/snabbswitch,fhanik/snabbswitch,fhanik/snabbswitch,kellabyte/snabbswitch,snabbnfv-goodies/snabbswitch,kellabyte/snabbswitch,plajjan/snabbswitch,wingo/snabb,Igalia/snabb,justincormack/snabbswitch,snabbco/snabb,alexandergall/snabbswitch,Igalia/snabbswitch,dwdm/snabbswitch,dpino/snabbswitch,dpino/snabb,wingo/snabbswitch,snabbco/snabb,heryii/snabb,eugeneia/snabb,dpino/snabb,Igalia/snabbswitch,aperezdc/snabbswitch,xdel/snabbswitch,lukego/snabb,aperezdc/snabbswitch,mixflowtech/logsensor,Igalia/snabb,dwdm/snabbswitch,aperezdc/snabbswitch,pavel-odintsov/snabbswitch,fhanik/snabbswitch,dpino/snabbswitch,snabbco/snabb,virtualopensystems/snabbswitch,mixflowtech/logsensor,lukego/snabb,alexandergall/snabbswitch,eugeneia/snabb,alexandergall/snabbswitch,eugeneia/snabb,wingo/snabb,pavel-odintsov/snabbswitch,lukego/snabbswitch,heryii/snabb,snabbco/snabb,dpino/snabb,pirate/snabbswitch,alexandergall/snabbswitch,snabbco/snabb,xdel/snabbswitch,xdel/snabbswitch,hb9cwp/snabbswitch,snabbnfv-goodies/snabbswitch,Igalia/snabbswitch,wingo/snabb,justincormack/snabbswitch,mixflowtech/logsensor,SnabbCo/snabbswitch,andywingo/snabbswitch,hb9cwp/snabbswitch,dpino/snabb,kbara/snabb,dwdm/snabbswitch,eugeneia/snabbswitch,snabbco/snabb,andywingo/snabbswitch,eugeneia/snabbswitch,wingo/snabbswitch,kbara/snabb,snabbco/snabb,kbara/snabb,pirate/snabbswitch,aperezdc/snabbswitch,dpino/snabbswitch,alexandergall/snabbswitch,virtualopensystems/snabbswitch,kellabyte/snabbswitch,wingo/snabb,plajjan/snabbswitch,lukego/snabbswitch,justincormack/snabbswitch,snabbco/snabb,mixflowtech/logsensor,eugeneia/snabb,kbara/snabb,mixflowtech/logsensor,javierguerragiraldez/snabbswitch,lukego/snabbswitch,wingo/snabb,Igalia/snabb,virtualopensystems/snabbswitch,eugeneia/snabb,Igalia/snabb,javierguerragiraldez/snabbswitch,Igalia/snabb,heryii/snabb,wingo/snabb,eugeneia/snabbswitch,javierguerragiraldez/snabbswitch,eugeneia/snabb,SnabbCo/snabbswitch,pavel-odintsov/snabbswitch,alexandergall/snabbswitch,Igalia/snabb,kbara/snabb,kbara/snabb,lukego/snabb,dpino/snabb