update to latest version of skarnet.org software

Laurent Bercot requested to merge skaware.20210109 into master

Major skalibs release, so all the updates must be done at the same time. This branch updates: skalibs, utmps, execline, s6, s6-linux-init, s6-rc, s6-dns, s6-networking, s6-portable-utils, s6-linux-utils, bncm, mdevd. Also makes sure sysvinit invokes s6 with the correct options, when s6 runs under sysvinit. The individuals commit are a mess because I'm an idiot, but in the end everything should be working.

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