selftests: net: bpf_offload: print loaded programs on mismatch

selftests: net: bpf_offload: print loaded programs on mismatch

The test sometimes fails due to an unexpected number of loaded programs. e.g

  FAIL: 2 BPF programs loaded, expected 1
    File "/usr/libexec/kselftests/net/./bpf_offload.py", line 940, in <module>
      progs = bpftool_prog_list(expected=1)
    File "/usr/libexec/kselftests/net/./bpf_offload.py", line 187, in bpftool_prog_list
      fail(True, "%d BPF programs loaded, expected %d" %
    File "/usr/libexec/kselftests/net/./bpf_offload.py", line 89, in fail
      tb = "".join(traceback.extract_stack().format())

However, the logs do not show which programs were actually loaded, making it
difficult to debug the failure.

Add printing of the loaded programs when a mismatch is detected to help
troubleshoot such errors. The list is printed on a new line to avoid breaking
the current log format.

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/20250819073348.387972-1-liuhangbin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>