stf flapping in/out of "tentative": patches for 11.2

[Mark Johnston]

On Sun, Nov 25, 2018 at 02:24:47PM -0500, Viktor Dukhovni wrote:
> 
> Not sure what's required to get these adopted upstream.  My stf0
> interface was still flapping in/out of "tentative" with 11.2, so
> I applied essentially the same patches as for 11.1.

Just a follow-up for the archives: a variant of the patch was committed
to head in r345739 and should appear in the stable branches in a few
weeks.