set nix bld ssh to throughput optimized

nixosModules/distributed-builds.nix

@@ -134,6 +134,8 @@ in
                 Match originalhost ${lib.concatStringsSep "," names} user ${buildUser}
                   IdentityFile ${clientSshKeyPath}
                   IdentitiesOnly yes
+                  IPQoS throughput
+                  ServerAliveInterval 60
               ''
             ) buildServerDevices
           );