fix: do not claim service control QTS cannot do

QnapQtsDriver inherits LinuxDriver, which now has manage_service() through
napalm-device-types' SystemdServicesMixin. QTS has no systemd, so every
action would fail. manage_service = None makes every capability check --
is manage_service callable -- answer no, so netOrk offers no controls that
cannot work.

tests/test_qnap_qts.py

@@ -182,3 +182,13 @@ class TestDockerBinDiscovery:
     def test_docker_bin_hook_returns_the_discovered_path(self, driver):
         driver._docker_path = "/opt/docker"
         assert driver._docker_bin() == "/opt/docker"
+
+
+def test_services_cannot_be_controlled():
+    """QTS has no systemd: the systemctl actions inherited from LinuxDriver would
+    fail on every unit, so the driver says it cannot control services at all --
+    which is what every capability check asks (is ``manage_service`` callable?)."""
+    from napalm_linux.linux import LinuxDriver
+
+    assert callable(getattr(LinuxDriver, "manage_service", None))
+    assert not callable(getattr(QnapQtsDriver, "manage_service", None))