samples/bpf: xdp_redirect_cpu: Load a eBPF program on cpumap

Extend xdp_redirect_cpu_{usr,kern}.c adding the possibility to load
a XDP program on cpumap entries. The following options have been added:
- mprog-name: cpumap entry program name
- mprog-filename: cpumap entry program filename
- redirect-device: output interface if the cpumap program performs a
  XDP_REDIRECT to an egress interface
- redirect-map: bpf map used to perform XDP_REDIRECT to an egress
  interface
- mprog-disable: disable loading XDP program on cpumap entries

Add xdp_pass, xdp_drop, xdp_redirect stats accounting

Co-developed-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/aa5a9a281b9dac425620fdabe82670ffb6bbdb92.1594734381.git.lorenzo@kernel.org