bpf: re-fix skip write only files in debugfs

Commit 5bc60de50d ("selftests: bpf: Don't try to read files without
read permission") got reverted as the fix was not working as expected
and real fix came in via 8101e06941 ("selftests: bpf: Skip write
only files in debugfs"). When bpf-next got merged into net-next, the
test_offload.py had a small conflict. Fix the resolution in ae8a76fb8b
iby not reintroducing 5bc60de50d again.

Fixes: ae8a76fb8b ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/bpf/test_offload.py

@@ -314,7 +314,10 @@ class DebugfsDir:
                 continue
 
             p = os.path.join(path, f)
-            if os.path.isfile(p) and os.access(p, os.R_OK):
+            if not os.stat(p).st_mode & stat.S_IRUSR:
+                continue
+
+            if os.path.isfile(p):
                 _, out = cmd('cat %s/%s' % (path, f))
                 dfs[f] = out.strip()
             elif os.path.isdir(p):