NETMAP_BDG_VNET_HDR: report error when could not find netmap adapter
NETMAP_BDG_VNET_HDR: report error when could not find netmap adapter

This is necessary to tell the user (e.g. the Hypervisor) that
virtio-net header is not supported on the requested netmap port.

luigirizzo/netmap,luigirizzo/netmap,luigirizzo/netmap,luigirizzo/netmap,luigirizzo/netmap