selftests: drv-net: Set shell=True for sysfs writes in devlink_rate_tc_bw.py

Commit 7c32f7a2d3db ("selftests: net: py: don't default to shell=True")
changed the cmd() helper to avoid spawning a shell unless explicitly
requested.

The devlink_rate_tc_bw test enables SR-IOV by writing to the
sriov_numvfs sysfs attribute using redirection. Without shell=True the
redirection is not interpreted and the VF device never appears,
causing the test to fail.

Fix by explicitly passing shell=True in the two places that update
sriov_numvfs.

Signed-off-by: Carolina Jubran <cjubran@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Reviewed-by: Nimrod Oren <noren@nvidia.com>
Link: https://patch.msgid.link/20251130091938.4109055-5-cjubran@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: cjubran

tools/testing/selftests/drivers/net/hw/devlink_rate_tc_bw.py

@@ -117,8 +117,8 @@ def setup_vf(cfg, set_tc_mapping=True):
     except Exception as exc:
         raise KsftSkipEx(f"Failed to enable switchdev mode on {cfg.pci}") from exc
     try:
-        cmd(f"echo 1 > /sys/class/net/{cfg.ifname}/device/sriov_numvfs")
-        defer(cmd, f"echo 0 > /sys/class/net/{cfg.ifname}/device/sriov_numvfs")
+        cmd(f"echo 1 > /sys/class/net/{cfg.ifname}/device/sriov_numvfs", shell=True)
+        defer(cmd, f"echo 0 > /sys/class/net/{cfg.ifname}/device/sriov_numvfs", shell=True)
     except Exception as exc:
         raise KsftSkipEx(f"Failed to enable SR-IOV on {cfg.ifname}") from exc