cli: fix setting 'slave-type' for nmcli connection add type *-slave

$ nmcli connection add type bond-slave ifname eth1 con-name bond0.0 master nm-bond
  Error: Failed to add 'bond0.0' connection: connection.slave-type: Cannot set 'master' without 'slave-type'

Fixes: 8ad218e71c

clients/cli/connections.c

@@ -4783,6 +4783,9 @@ complete_slave (NMSettingConnection *s_con,
 			                     _("Error: redundant 'master' option."));
 			return FALSE;
 		}
+		g_object_set (s_con,
+		              NM_SETTING_CONNECTION_SLAVE_TYPE, slave_type,
+		              NULL);
 		return TRUE;
 	}