nixos/tests/ferm: disable dhcpcd

The test failed in one run on Hydra, logs look like
dhcpcd changed ipv6 routing at just the wrong time.
Disable dhcpcd. It's not needed, the test uses static IPs anyway.

nixos/tests/ferm.nix

@@ -11,6 +11,7 @@ import ./make-test.nix ({ pkgs, ...} : {
         with pkgs.lib;
         {
           networking = {
+            dhcpcd.enable = false;
             interfaces.eth1.ipv6.addresses = mkOverride 0 [ { address = "fd00::2"; prefixLength = 64; } ];
             interfaces.eth1.ipv4.addresses = mkOverride 0 [ { address = "192.168.1.2"; prefixLength = 24; } ];
           };
@@ -20,6 +21,7 @@ import ./make-test.nix ({ pkgs, ...} : {
         with pkgs.lib;
         {
           networking = {
+            dhcpcd.enable = false;
             interfaces.eth1.ipv6.addresses = mkOverride 0 [ { address = "fd00::1"; prefixLength = 64; } ];
             interfaces.eth1.ipv4.addresses = mkOverride 0 [ { address = "192.168.1.1"; prefixLength = 24; } ];
           };
@@ -51,7 +53,7 @@ import ./make-test.nix ({ pkgs, ...} : {
     ''
       startAll;
 
-      $client->waitForUnit("network.target");
+      $client->waitForUnit("network-online.target");
       $server->waitForUnit("ferm.service");
       $server->waitForUnit("nginx.service");
       $server->waitUntilSucceeds("ss -ntl | grep -q 80");