MT#57501 enumeration value 'NonHold' not handled in switch

Add handling of the `ZeroedHold` and also handle the default action
in the switch inside `CallLeg::updateLocalSdp()`.

This eliminates the warning:

     CallLeg.cpp: In member function 'virtual void CallLeg::updateLocalSdp(AmSdp&)':
     CallLeg.cpp:2019:15: warning: enumeration value 'NonHold' not handled in switch [-Wswitch]
      2019 |         switch(hold_method_requested)
           |               ^
     CallLeg.cpp:2019:15: warning: enumeration value 'ZeroedHold' not handled in switch [-Wswitch]

Change-Id: If0eebda2182b44aa591eb9aedd43481c94788b13

apps/sbc/CallLeg.cpp

@@ -1860,6 +1860,11 @@ void CallLeg::updateLocalSdp(AmSdp &sdp)
             DBG("On hold has been previously requested and must be held further\n");
             DBG("This SDP is prepared to be sent with the a=inactive\n");
             break;
+          case ZeroedHold:
+            DBG("On hold has been previously requested, but will be not held further (zeroed hold)\n");
+            break;
+          default:
+            break; /* do nothing, this handles the compiler's warning that NonHold is not mentioned in switch */
         }
       }
     }