selftests/bpf: Add launch time request to xdp_hw_metadata

Add launch time hardware offload request to xdp_hw_metadata. Users can
configure the delta of launch time relative to HW RX-time using the "-l"
argument. By default, the delta is set to 0 ns, which means the launch time
is disabled. By setting the delta to a non-zero value, the launch time
hardware offload feature will be enabled and requested. Additionally, users
can configure the Tx Queue to be enabled with the launch time hardware
offload using the "-L" argument. By default, Tx Queue 0 will be used.

Signed-off-by: Song Yoong Siang <yoong.siang.song@intel.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250216093430.957880-3-yoong.siang.song@intel.com