nixos/sshd: fix socket activated ports when using ListenAddress

Noticed that issue while reviewing #275633: when declaring
`ListenAddress host` without a port, all ports declared by
`Port`/`cfg.ports` will be used with `host` according to
`sshd_config(5)`.

However, if this is done and socket activation is used, only a socket
for port 22 is created instead of a sockets for each port from
`Port`/`cfg.ports`. This patch corrects that behavior.

Also added a regression test for this case.

nixos/modules/services/networking/ssh/sshd.nix

@@ -600,7 +600,11 @@ in
           { description = "SSH Socket";
             wantedBy = [ "sockets.target" ];
             socketConfig.ListenStream = if cfg.listenAddresses != [] then
-              map (l: "${l.addr}:${toString (if l.port != null then l.port else 22)}") cfg.listenAddresses
+              concatMap
+                ({ addr, port }:
+                  if port != null then [ "${addr}:${toString port}" ]
+                  else map (p: "${addr}:${toString p}") cfg.ports)
+                cfg.listenAddresses
             else
               cfg.ports;
             socketConfig.Accept = true;