selftests/bpf: Fix xdp_do_redirect failure with 64KB page size

On arm64 with 64KB page size, the selftest xdp_do_redirect failed like
below:
  ...
  test_xdp_do_redirect:PASS:pkt_count_tc 0 nsec
  test_max_pkt_size:PASS:prog_run_max_size 0 nsec
  test_max_pkt_size:FAIL:prog_run_too_big unexpected prog_run_too_big: actual -28 != expected -22

With 64KB page size, the xdp frame size will be much bigger so
the existing test will fail.

Adjust various parameters so the test can also work on 64K page size.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20250612035042.2208630-1-yonghong.song@linux.dev


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