virtio-net: bind systematically on all non blacklisted virtio-net devices

[Franck Baudin <franck.baudin@qosmos.com>]

Hi,

virtio-net driver bind on all virtio-net devices, even if the devices 
are used by the kernel (leading to kernel soft-lookup/panic). One way 
around is to blacklist the ports in use by Linux. This is the case since 
v2.0.0, in fact since commit da978dfdc43b59e290a46d7ece5fd19ce79a1162 
and the removal of the RTE_PCI_DRV_NEED_MAPPING driver flag.

Questions:
     1/ Is it the expected behaviour?
     2/ Why is it different from vmxnet3 pmd? In other words, should't 
we re-add the RTE_PCI_DRV_NEED_MAPPING to virtio pmd or remove it from 
pmxnet3 pmd?
     3/ If this is the expected behaviour, shouldn't we update 
dpdk_nic_bind.py (binding status irrelevant for virtio) tool and the 
documentation (mentioning igb_uio while misleading and useless)?

Thanks!

Best Regards,
Franck