Remove Sixxs as a tunnel provider. Service will be shutting down in a couple of months. https://www.sixxs.net/sunset/ PR: 218624 Submitted by: freebsd AT ccc DOT de Approved by: bcr (mentor) Differential Revision: https://reviews.freebsd.org/D10453
head/en_US.ISO8859-1/books/handbook/advanced-networking/chapter.xml