netdev: introduce new NETIF_F_HW_SWITCH_OFFLOAD feature flag for switch device offloads

This is a high level feature flag for all switch asic offloads

switch drivers set this flag on switch ports. Logical devices like
bridge, bonds, vxlans can inherit this flag from their slaves/ports.

The patch also adds the flag to NETIF_F_ONE_FOR_ALL, so that it gets
propagated to the upperdevices (bridges and bonds).

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>