[Fix] CavityResonator with Ncav

Changing Ncav after initialization now change the total shunt impedance Rs

tracking/rf.py

@@ -559,12 +559,11 @@ class CavityResonator():
     @Rs_per_cavity.setter
     def Rs_per_cavity(self, value):
         self._Rs_per_cavity = value
-        self._Rs = self.Rs_per_cavity * self.Ncav
 
     @property
     def Rs(self):
         """Shunt impedance [ohm]"""
-        return self._Rs
+        return self.Rs_per_cavity * self.Ncav
 
     @Rs.setter
     def Rs(self, value):