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.

napalm_qnap_qts/qnap_qts.py

@@ -68,6 +68,12 @@ class QnapQtsDriver(StorageDriver, HypervisorDriver, LinuxDriver):
     driver_name = "qnap_qts"
     NETMIKO_DEVICE_TYPE = "linux"
 
+    #: QTS has no systemd, so the systemctl actions LinuxDriver inherits from
+    #: napalm-device-types' SystemdServicesMixin would fail on every unit. None
+    #: makes every "can it control services?" check -- is ``manage_service``
+    #: callable -- answer no, rather than offering buttons that cannot work.
+    manage_service = None  # type: ignore[assignment]
+
     SNMP_OBJECT_ID_PREFIX = QNAP_ENTERPRISE_OID
     SNMP_FINGERPRINT = [
         FingerprintRule("qnap", weight=9.0),