[VOL-4080] Extend GetExtValue api to read transceiver rx-power on demand.

Change-Id: I3b9728f9eeb9c5b17df41774d21bd16ddc7b69c0
diff --git a/internal/pkg/core/openolt.go b/internal/pkg/core/openolt.go
index 51ce314..436d67a 100644
--- a/internal/pkg/core/openolt.go
+++ b/internal/pkg/core/openolt.go
@@ -433,6 +433,8 @@
 			return handler.getOltPortCounters(ctx, reqType.OltPortInfo), nil
 		case *extension.GetValueRequest_OnuPonInfo:
 			return handler.getOnuPonCounters(ctx, reqType.OnuPonInfo), nil
+		case *extension.GetValueRequest_RxPower:
+			return handler.getRxPower(ctx, reqType.RxPower), nil
 		default:
 			return errResp(extension.GetValueResponse_ERROR, extension.GetValueResponse_UNSUPPORTED), nil
 		}