selftests/bpf: Convert xdp_hw_metadata to XDP_USE_NEED_WAKEUP

This is the recommended way to run AF_XDP, so let's use it in the test.

Also, some unrelated changes to now blow up the log too much:
- change default mode to zerocopy and add -c to use copy mode
- small fixes for the flags/sizes/prints
- add print_tstamp_delta to print timestamp + reference

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20231127190319.1190813-13-sdf@google.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>