bpf, test_offload.py: Skip base maps without names

The test fails:

# ./test_offload.py
[...]
Test bpftool bound info reporting (own ns)...
FAIL: 3 BPF maps loaded, expected 2
File "/root/bpf-next/tools/testing/selftests/bpf/./test_offload.py", line 1177, in <module>
check_dev_info(False, "")
File "/root/bpf-next/tools/testing/selftests/bpf/./test_offload.py", line 645, in check_dev_info
maps = bpftool_map_list(expected=2, ns=ns)
File "/root/bpf-next/tools/testing/selftests/bpf/./test_offload.py", line 190, in bpftool_map_list
fail(True, "%d BPF maps loaded, expected %d" %
File "/root/bpf-next/tools/testing/selftests/bpf/./test_offload.py", line 86, in fail
tb = "".join(traceback.extract_stack().format())

Some base maps do not have names and they cannot be added due to compatibility
with older kernels, see [0]. So, just skip the unnamed maps.

[0] https://lore.kernel.org/bpf/[e-mail]/

Signed-off-by: Yauheni Kaliuta <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Quentin Monnet <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/test_offload.py

···
 def bpftool_map_list(expected=None, ns=""):
     _, maps = bpftool("map show", JSON=True, ns=ns, fail=True)
     # Remove the base maps
-    maps = [m for m in maps if m not in base_maps and m.get('name') not in base_map_names]
+    maps = [m for m in maps if m not in base_maps and m.get('name') and m.get('name') not in base_map_names]
     if expected is not None:
         if len(maps) != expected:
             fail(True, "%d BPF maps loaded, expected %d" %