Why do I see "open_socket_in(): socket() call failed: Address family not supported by protocol" in log.smbd?

Issue

• Why do I see "open_socket_in(): socket() call failed: Address family not supported by protocol" in log.smbd?

Sample log of /var/log/samba/log.smbd:

[2017/10/12 10:58:52.455507,  0] ../lib/util/become_daemon.c:124(daemon_ready)
  STATUS=daemon 'smbd' finished starting up and ready to serve connections
[2017/10/12 10:58:52.461372,  0] ../source3/lib/util_sock.c:334(open_socket_in)
  open_socket_in(): socket() call failed: Address family not supported by protocol
[2017/10/12 10:58:52.461464,  0] ../source3/smbd/server.c:1080(smbd_open_one_socket)
  smbd_open_one_socket: open_socket_in: Address family not supported by protocol
[2017/10/12 10:58:52.465569,  0] ../source3/lib/util_sock.c:334(open_socket_in)
  open_socket_in(): socket() call failed: Address family not supported by protocol
[2017/10/12 10:58:52.465595,  0] ../source3/smbd/server.c:1080(smbd_open_one_socket)
  smbd_open_one_socket: open_socket_in: Address family not supported by protocol