net: dsa: cpu_dp->orig_ethtool_ops might be NULL

net: dsa: cpu_dp->orig_ethtool_ops might be NULL

In theory this would have been seen by now, but it seems that all
drivers used as DSA conduit interfaces thus far have had ethtool_ops
set, and it's hard to even find modern Ethernet drivers (and not VF
ones) which don't use ethtool.

Here is the unfiltered list of drivers which register any sort of
net_device but don't set its ethtool_ops pointer. I don't think any of
them 'risks' being used as a DSA conduit, maybe except for moxart,
rnpbge and icssm, I'm not sure.

- drivers/net/can/dev/dev.c
- drivers/net/wwan/qcom_bam_dmux.c
- drivers/net/wwan/t7xx/t7xx_netdev.c
- drivers/net/arcnet/arcnet.c
- drivers/net/hamradio/
- drivers/net/slip/slip.c
- drivers/net/ethernet/ezchip/nps_enet.c
- drivers/net/ethernet/moxa/moxart_ether.c
- drivers/net/ethernet/wangxun/txgbevf/txgbevf_main.c
- drivers/net/ethernet/wangxun/ngbevf/ngbevf_main.c
- drivers/net/ethernet/huawei/hinic3/hinic3_main.c
- drivers/net/ethernet/i825xx/
- drivers/net/ethernet/ti/icssm/icssm_prueth.c
- drivers/net/ethernet/seeq/
- drivers/net/ethernet/litex/litex_liteeth.c
- drivers/net/ethernet/sunplus/spl2sw_driver.c
- drivers/net/ethernet/mucse/rnpgbe/rnpgbe_main.c
- drivers/net/ipa/
- drivers/net/wireless/microchip/wilc1000/
- drivers/net/wireless/mediatek/mt76/dma.c
- drivers/net/wireless/ath/ath12k/
- drivers/net/wireless/ath/ath11k/
- drivers/net/wireless/ath/ath6kl/
- drivers/net/wireless/ath/ath10k/
- drivers/net/wireless/intel/iwlwifi/pcie/gen1_2/trans.c
- drivers/net/wireless/virtual/mac80211_hwsim.c
- drivers/net/wireless/quantenna/qtnfmac/pcie/pcie.c
- drivers/net/wireless/realtek/rtw89/core.c
- drivers/net/wireless/realtek/rtw88/pci.c
- drivers/net/caif/
- drivers/net/plip/
- drivers/net/wan/
- drivers/net/mctp/
- drivers/net/ppp/
- drivers/net/thunderbolt/

Nonetheless, it's good for the framework not to make such assumptions,
and not panic when coming across such kind of host device in the future.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20251122112311.138784-2-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>