From: Eric Dumazet <redacted>
Date: Thu, 8 Mar 2018 10:05:12 -0800

Another problematic legacy behavior is the automatic creation of
fallback tunnels, which hurts netns creation/deletion.

Some environments want to create a netns for every job/task, and they
do not care if the init netns has these tunnels or not.

We have a local patch adding yet another knob to control this, since
it saves a lot of cpu cycles (about 10ms per netns create/delete pair
here)

Yeah, understood.  At small scale the current behavior maybe made
sense, but these days it really doesn't.

No objections to the knob if you want to submit it.