From: Yuval Mintz <redacted>
Date: Wed, 31 Dec 2014 08:35:36 +0200

When register_netdevice() is called, netdevice's vlan filtering feature
and supplied callbacks are checked to see the vlan implementation is
not buggy.
This adds an additional test - see that the vlan_features were filled
correctly, as the vlan devices inherits those as its own features;
Incorrect values set there would later prevent the vlan interface from being
registered itself [as it doesn't implement the filtering ndos].

Signed-off-by: Yuval Mintz <redacted>

 ...

Not sure why take such a defensive approach regarding this feature.
Perhaps it would have been better to simply remove these checks altogether.

I guess this is fine as a defensive test, so I'll apply this.

But do you actually know of any devices which have violated this rule
either now or in the past?  I quickly tried to audit the entire tree
for this right now and found no problems.