selftests/bpf: Add xdpdrv mode for test_xdp_redirect

This patch add xdpdrv mode for test_xdp_redirect.sh since veth has support
native mode. After update here is the test result:

  # ./test_xdp_redirect.sh
  selftests: test_xdp_redirect xdpgeneric [PASS]
  selftests: test_xdp_redirect xdpdrv [PASS]

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: William Tu <u9012063@gmail.com>
Link: https://lore.kernel.org/bpf/20200729085658.403794-1-liuhangbin@gmail.com