selftests/bpf: Bring test_offload.py back to life

Bpftool has new extra libbpf_det_bind probing map we need to exclude.
Also skip trying to load netdevsim modules if it's already loaded (builtin).

v2:
- drop iproute2->bpftool changes (Toke)
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20221206232739.2504890-1-sdf@google.com

tools/testing/selftests/bpf/test_offload.py

@@ -769,12 +769,14 @@ skip(ret != 0, "bpftool not installed")
 base_progs = progs
 _, base_maps = bpftool("map")
 base_map_names = [
-    'pid_iter.rodata' # created on each bpftool invocation
+    'pid_iter.rodata', # created on each bpftool invocation
+    'libbpf_det_bind', # created on each bpftool invocation
 ]
 
 # Check netdevsim
-ret, out = cmd("modprobe netdevsim", fail=False)
-skip(ret != 0, "netdevsim module could not be loaded")
+if not os.path.isdir("/sys/bus/netdevsim/"):
+    ret, out = cmd("modprobe netdevsim", fail=False)
+    skip(ret != 0, "netdevsim module could not be loaded")
 
 # Check debugfs
 _, out = cmd("mount")