{enb,ms}_srs: Add DL QAM-256 support

Due to the integration of DL-QAM256 another table for DL max rates is needed.
Therefore, I added the parameter 'qam256' to the feature list in the resource.cfg.

The patch also enables the correct UE settings in the config file.

Change-Id: I2d34395449cdcfb31db66ea887d9adbee551e757
diff --git a/src/osmo_gsm_tester/obj/ms_srs.py b/src/osmo_gsm_tester/obj/ms_srs.py
index a3505c8..610d3e6 100644
--- a/src/osmo_gsm_tester/obj/ms_srs.py
+++ b/src/osmo_gsm_tester/obj/ms_srs.py
@@ -128,6 +128,9 @@
         # Collect KPIs for each TC
         self.testenv.test().set_kpis(self.get_kpis())
 
+    def features(self):
+        return self._conf.get('features', [])
+
     def scp_back_metrics(self, raiseException=True):
         ''' Copy back metrics only if they have not been copied back yet '''
         if not self.have_metrics_file: