COM audio did not tune in (voice room) if channel was already selected at startup

Reason was: hardcoded channel spacing to 8.33kHz

As a result changed to channel spacing based on COM unit, which could also be changed at runtime

* the issue itself was in own aircraft context
* added functions for channel spacing
* changed to COM unit channel spacing (instead of hardcoded spacing)

src/blackmisc/aviation/atcstationlist.cpp

@@ -39,6 +39,14 @@ namespace BlackMisc
             });
         }
 
+        CAtcStationList CAtcStationList::findIfComUnitTunedInChannelSpacing(const CComSystem &comUnit) const
+        {
+            return this->findBy([&](const CAtcStation & atcStation)
+            {
+                return atcStation.isComUnitTunedInChannelSpacing(comUnit);
+            });
+        }
+
         CAtcStationList CAtcStationList::findIfFrequencyIsWithinSpacing(const CFrequency &frequency, CComSystem::ChannelSpacing spacing)
         {
             if (frequency.isNull()) { return CAtcStationList(); }