NetworkManager reports error 'Failed to enable/disable userspace IPv6LL address handling.'

Issue

• NetworkManager is logging these errors about IPv6:

  # journalctl --no-pager -u NetworkManager -p warning
  -- Logs begin at Tue 2018-10-23 03:49:08 EDT, end at Tue 2018-10-23 03:49:24 EDT. --
  Oct 23 03:49:13 localhost NetworkManager[698]: <warn>  [1540280953.6224] platform-linux: do-change-link[2]: failure changing link: failure 97 (Address family not supported by protocol)
  Oct 23 03:49:13 localhost NetworkManager[698]: <warn>  [1540280953.6230] device (eth0): failed to enable userspace IPv6LL address handling (unspecified)
  Oct 23 03:49:13 localhost NetworkManager[698]: <warn>  [1540280953.6890] platform-linux: do-change-link[2]: failure changing link: failure 97 (Address family not supported by protocol)
  Oct 23 03:49:13 localhost NetworkManager[698]: <warn>  [1540280953.6894] device (eth0): failed to enable userspace IPv6LL address handling (unspecified)
  Oct 23 03:49:14 localhost NetworkManager[698]: <warn>  [1540280954.1981] platform-linux: do-change-link[2]: failure changing link: failure 97 (Address family not supported by protocol)
  Oct 23 03:49:14 localhost NetworkManager[698]: <warn>  [1540280954.1982] device (eth0): failed to enable userspace IPv6LL address handling (unspecified)
  Oct 23 03:49:14 localhost NetworkManager[698]: <error> [1540280954.2106] device (eth0): addrconf6: failed to start neighbor discovery: failure creating libndp socket: Address family not supported by protocol (97)
  

• Another error message pattern

  Jan 27 01:24:19 localhost NetworkManager[11936]: <warn>  [1580106259.1885] device (bond0): failed to enable userspace IPv6LL address handling (unspecified)