selftests: drv-net: stats: use skip instead of xfail for unsupported features

XFAIL is considered a form of a pass by our CI. For HW devices returning
XFAIL for unsupported features is counter-productive because our CI
knows not to expect any HW test to pass until it sees 10 passes in a row.
If we return xfail the test shows up as pass even if the device doesn't
support the feature. netdevsim supports all features necessary for
the stats test so there is no concern about running the test in SW mode.

Make the test skip rather than xfail if driver doesn't support FEC or pause.

Link: https://patch.msgid.link/20250620161109.2146242-3-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/stats.py

@@ -10,7 +10,7 @@ import subprocess
 import time
 from lib.py import ksft_run, ksft_exit, ksft_pr
 from lib.py import ksft_ge, ksft_eq, ksft_is, ksft_in, ksft_lt, ksft_true, ksft_raises
-from lib.py import KsftSkipEx, KsftXfailEx, KsftFailEx
+from lib.py import KsftSkipEx, KsftFailEx
 from lib.py import ksft_disruptive
 from lib.py import EthtoolFamily, NetdevFamily, RtnlFamily, NlError
 from lib.py import NetDrvEnv
@@ -31,7 +31,7 @@ def check_pause(cfg) -> None:
         ethnl.pause_get({"header": {"dev-index": cfg.ifindex}})
     except NlError as e:
         if e.error == errno.EOPNOTSUPP:
-            raise KsftXfailEx("pause not supported by the device") from e
+            raise KsftSkipEx("pause not supported by the device") from e
         raise
 
     data = ethnl.pause_get({"header": {"dev-index": cfg.ifindex,
@@ -49,7 +49,7 @@ def check_fec(cfg) -> None:
         ethnl.fec_get({"header": {"dev-index": cfg.ifindex}})
     except NlError as e:
         if e.error == errno.EOPNOTSUPP:
-            raise KsftXfailEx("FEC not supported by the device") from e
+            raise KsftSkipEx("FEC not supported by the device") from e
         raise
 
     data = ethnl.fec_get({"header": {"dev-index": cfg.ifindex,