virtio_net: Extend virtio to use VF datapath when available

virtio_net: Extend virtio to use VF datapath when available

This patch enables virtio_net to switch over to a VF datapath when STANDBY
feature is enabled and a VF netdev is present with the same MAC address.
It allows live migration of a VM with a direct attached VF without the need
to setup a bond/team between a VF and virtio net device in the guest.

It uses the API that is exported by the net_failover driver to create and
and destroy a master failover netdev. When STANDBY feature is enabled, an
additional netdev(failover netdev) is created that acts as a master device
and tracks the state of the 2 lower netdevs. The original virtio_net netdev
is marked as 'standby' netdev and a passthru device with the same MAC is
registered as 'primary' netdev.

The hypervisor needs to unplug the VF device from the guest on the source
host and reset the MAC filter of the VF to initiate failover of datapath
to virtio before starting the migration. After the migration is completed,
the destination hypervisor sets the MAC filter on the VF and plugs it back
to the guest to switch over to VF datapath.

This patch is based on the discussion initiated by Jesse on this thread.
https://marc.info/?l=linux-virtualization&m=151189725224231&w=2

Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit ba5e4426e80e0435358c7117c339e6a4c22c34ad)
Orabug: 28122104
Signed-off-by: Vijay Balakrishna <vijay.balakrishna@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
(cherry picked from commit cf863ad81d0bcdefe6520fea20c81df26decef4f)
Signed-off-by: Vijay Balakrishna <vijay.balakrishna@oracle.com>
Reviewed-by: Si-Wei Liu <si-wei.liu@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	drivers/net/Kconfig
(merge during cherry-pick need manual intervention to resolve)
	drivers/net/virtio_net.c
(manual merge required as file differes between UEK5 and UEK4)

Signed-off-by: Brian Maly <brian.maly@oracle.com>