mlxsw: ethtool: Prepare for RTNL-less ethtool operations

A subsequent patch is going to make the driver ops-locked and allow
ethtool operations to run without RTNL. In preparation for this change,
tell the core about a couple of ethtool operations that should remain
under RTNL:

1. Set pause parameters: Configures the port's headroom buffer which is
also configured by RTNL-only paths such as DCB and qdisc. These paths
can probably be converted to acquire the netdev instance lock, but this
operation in not frequently called (unlike stats query), so avoid the
added complexity for now.

2. Get link state: Calls ethtool_op_get_link() which requires RTNL. See
commit 1105ef941c ("net: ethtool: keep rtnl_lock for ops using
ethtool_op_get_link()").

All the other operations do not access shared resources, do not invoke
helpers that require RTNL or already have the appropriate locking in
place.

Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260708123933.1303291-3-idosch@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c

@@ -1262,6 +1262,8 @@ mlxsw_sp_set_module_power_mode(struct net_device *dev,
 
 const struct ethtool_ops mlxsw_sp_port_ethtool_ops = {
 	.cap_link_lanes_supported	= true,
+	.op_needs_rtnl			= ETHTOOL_OP_NEEDS_RTNL_SPAUSEPARAM |
+					  ETHTOOL_OP_NEEDS_RTNL_GLINK,
 	.get_drvinfo			= mlxsw_sp_port_get_drvinfo,
 	.get_link			= ethtool_op_get_link,
 	.get_link_ext_state		= mlxsw_sp_port_get_link_ext_state,