Fixing the BandwidthController unit test

The BandwidthController unit test cannot directly use gCtrl->trafficCtrl
to check if the bpf stats feature is avaliable. Rewrite the
getBpfStatsStatus() function of BandwidthController so it is also
functioning when in BandwidthController unit tests.

Bug: 72111305
Test: ./netd_unit_test
Change-Id: Ie60ed384b7f8d42b8e1f3417949d46895bea6572
diff --git a/server/BandwidthController.h b/server/BandwidthController.h
index c8dad99..efacdce 100644
--- a/server/BandwidthController.h
+++ b/server/BandwidthController.h
@@ -33,6 +33,7 @@
     BandwidthController();
 
     int setupIptablesHooks();
+    static bool getBpfStatsStatus();
 
     int enableBandwidthControl(bool force);
     int disableBandwidthControl();