ebpf: Added eBPF RSS loader.

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>
Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

configure

@@ -348,6 +348,7 @@ vhost_vsock="$default_feature"
 vhost_user="no"
 vhost_user_blk_server="auto"
 vhost_user_fs="$default_feature"
+bpf="auto"
 kvm="auto"
 hax="auto"
 hvf="auto"
@@ -1240,6 +1241,10 @@ for opt do
   ;;
   --enable-membarrier) membarrier="yes"
   ;;
+  --disable-bpf) bpf="disabled"
+  ;;
+  --enable-bpf) bpf="enabled"
+  ;;
   --disable-blobs) blobs="false"
   ;;
   --with-pkgversion=*) pkgversion="$optarg"
@@ -1878,6 +1883,7 @@ disabled with --disable-FEATURE, default is enabled if available
   vhost-user      vhost-user backend support
   vhost-user-blk-server    vhost-user-blk server support
   vhost-vdpa      vhost-vdpa kernel backend support
+  bpf             BPF kernel support
   spice           spice
   spice-protocol  spice-protocol
   rbd             rados block device (rbd)
@@ -6476,7 +6482,7 @@ if test "$skip_meson" = no; then
         -Dattr=$attr -Ddefault_devices=$default_devices \
         -Ddocs=$docs -Dsphinx_build=$sphinx_build -Dinstall_blobs=$blobs \
         -Dvhost_user_blk_server=$vhost_user_blk_server -Dmultiprocess=$multiprocess \
-        -Dfuse=$fuse -Dfuse_lseek=$fuse_lseek -Dguest_agent_msi=$guest_agent_msi \
+        -Dfuse=$fuse -Dfuse_lseek=$fuse_lseek -Dguest_agent_msi=$guest_agent_msi -Dbpf=$bpf\
         $(if test "$default_features" = no; then echo "-Dauto_features=disabled"; fi) \
 	-Dtcg_interpreter=$tcg_interpreter \
         $cross_arg \