Additional code that will be used for eBPF setting steering routine.

For now, that method supported only by Linux TAP.
Linux TAP uses TUNSETSTEERINGEBPF ioctl.

RSS program and Makefile to build it.
The bpftool used to generate '.h' file.
The data in that file may be loaded by libbpf.
EBPF compilation is not required for building qemu.
You can use Makefile if you need to regenerate rss.bpf.skeleton.h.

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>

Added function that loads RSS eBPF program.
Added stub functions for RSS eBPF loader.
Added meson and configuration options.

By default, eBPF feature enabled if libbpf is present in the build system.
libbpf checked in configuration shell script and meson script.

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>

if 'vhost_net_disabled' in the NetClientState of the
net device, get_vhost_net for TAP returns NULL. Network adapters
can use this ability to hide the vhost_net temporary between
resets in case some active features contradict with vhost.

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>

When RSS is enabled the device tries to load the eBPF program
to select RX virtqueue in the TUN. If eBPF can be loaded
the RSS will function also with vhost (works with kernel 5.8 and later).
Software RSS is used as a fallback with vhost=off when eBPF can't be loaded
or when hash population requested by the guest.
In case the RSS feature is present and acked by the guest but the ebpf
due to any reason can't be used with vhost, the virtio-net disables
vhost till next reset (or migration) and uses userspace virtio.
The same in case the hash report feature is acked by the guest (the
vhost can't support this feature currently).

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>

Also, added maintainers information.

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>