net: provide a default dev->ethtool_ops

Instead of forcing device drivers to provide empty ethtool_ops or tweak
net/core/ethtool.c again, we could provide a generic ethtool_ops.

This occurred to me when I wanted to add GSO support to GRE tunnels.
ethtool -k support should be generic for all drivers.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: Maciej Żenczykowski <maze@google.com>
Reviewed-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index bb42eb1..bbda819 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5974,6 +5974,8 @@
 	return queue;
 }
 
+static const struct ethtool_ops default_ethtool_ops;
+
 /**
  *	alloc_netdev_mqs - allocate network device
  *	@sizeof_priv:	size of private data to allocate space for
@@ -6061,6 +6063,8 @@
 
 	strcpy(dev->name, name);
 	dev->group = INIT_NETDEV_GROUP;
+	if (!dev->ethtool_ops)
+		dev->ethtool_ops = &default_ethtool_ops;
 	return dev;
 
 free_all: