[cups] (5 commits) ...Use upstream fix for driverd issue (bug #742989).

[Tim Waugh]

Summary of changes:

  0928f7c... Set BindIPv6Only=ipv6-only in systemd socket unit file as b (*)
  6085d5e... Increase client blocking timeout from 30s to 70s (bug #7447 (*)
  3f9aa63... Array handling fixes for Avahi poll implementation. (*)
  6a13918... Array handling fixes for DNSSDPrinters. (*)
  042f3d8... Use upstream fix for driverd issue (bug #742989). (*)

(*) This commit already existed in another branch; no separate mail sent