Merge remote-tracking branch 'nl6720/RouteMetric'

* nl6720/RouteMetric:
  configs/*/airootfs/etc/systemd/system/systemd-networkd-wait-online.service.d/wait-for-only-one-interface.conf: document why the drop-in file exists
  configs/releng/airootfs/etc/systemd/network/: move RouteMetric= from [DHCPv6] to [IPv6AcceptRA]
7 jobs for master in 31 minutes and 38 seconds (queued for 9 seconds)
Status Name Job ID Coverage
  Check
passed check #30114

00:00:14

 
  Build
passed build_long: [baseline iso] #30117
fast-single-thread

00:17:30

passed build_long: [baseline netboot] #30118
fast-single-thread

00:16:20

passed build_long: [releng iso] #30119
fast-single-thread

00:31:22

passed build_long: [releng netboot] #30120
fast-single-thread

00:30:04

passed build_short: [baseline bootstrap] #30115

00:12:41

passed build_short: [releng bootstrap] #30116

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