mod-gr-broker: add scenario to easily enable the GR broker

Change-Id: I4397e26713778721b7138b03b7a5f8f63f780d44
diff --git a/sysmocom/scenarios/mod-gr-broker.conf b/sysmocom/scenarios/mod-gr-broker.conf
new file mode 100644
index 0000000..6824ca8
--- /dev/null
+++ b/sysmocom/scenarios/mod-gr-broker.conf
@@ -0,0 +1,8 @@
+# Select GNU Radio broker for channel management
+modifiers:
+  enb:
+  - cell_list:
+    - dl_rfemu:
+       type: gnuradio_zmq
+    - dl_rfemu:
+       type: gnuradio_zmq