ssh module: ignore exit code when socket activated

sshd will at times fail when exiting. When socket activated, this will
leave a number of sshd@ service instances in the failed state, so we
simply ignore the error code if we are running socket activated.

Recommended by upstream:
http://systemd-devel.freedesktop.narkive.com/d0eapMCG/socket-activated-sshd-service-showing-up-as-a-failure-when-the-client-connection-fails

Fixes: #3279

Changed files
+1
nixos
modules
services
networking
ssh
+1
nixos/modules/services/networking/ssh/sshd.nix
···
serviceConfig =
{ ExecStart =
+
(optionalString cfg.startWhenNeeded "-") +
"${cfgc.package}/bin/sshd " + (optionalString cfg.startWhenNeeded "-i ") +
"-f ${pkgs.writeText "sshd_config" cfg.extraConfig}";
KillMode = "process";