Bug#968589: Need to restart internet connections upon upgrade, else no names can be resolved

[積丹尼 Dan Jacobson]

Nameserver running fine.

  # aptitude reinstall systemd
  Reinstalling systemd (246.3-1) over (246.3-1) ...

Nameserver now not running fine. Can only reach IP addresses. Can't
resolve names.

  poff; ifconfig ... down; sleep ...; ifconfig ... up; pon

fixed it this time. Didn't need full reboot.

See also
https://bugs.debian.org/cgi-bin/bugreport.cgi?att=1;bug=968589;filename=reportbug-systemd-backup-20200819-23352-5i1cr8wc.gz;msg=36