enb_amarisoft: add option to enable and configure DL AWGN channel

expose option to enable DL AWGN noise and make SNR configurable

Change-Id: Ib248e87e5abd855d4c974eab42ec40828c6e1d40
diff --git a/src/osmo_gsm_tester/obj/enb_amarisoft.py b/src/osmo_gsm_tester/obj/enb_amarisoft.py
index 4b24844..c7a9810 100644
--- a/src/osmo_gsm_tester/obj/enb_amarisoft.py
+++ b/src/osmo_gsm_tester/obj/enb_amarisoft.py
@@ -160,6 +160,8 @@
         self.enable_measurements = util.str2bool(values['enb'].get('enable_measurements', 'false'))
         config.overlay(values, dict(enb={'enable_measurements': self.enable_measurements}))
 
+        config.overlay(values, dict(enb={'enable_dl_awgn': util.str2bool(values['enb'].get('enable_dl_awgn', 'false'))}))
+
         # We need to set some specific variables programatically here to match IP addresses:
         if self._conf.get('rf_dev_type') == 'zmq':
             base_srate = self.num_prb2base_srate(self.num_prb())