srs_ue: adding num_carriers paramter and corresponding modifier

this allows to configure a UE to support multiple carriers

Change-Id: I4fa0a0c6e52efb17aa0b07e55abb5470d8028e8b
diff --git a/example/scenarios/mod-srsue-ncarriers@.conf b/example/scenarios/mod-srsue-ncarriers@.conf
new file mode 100644
index 0000000..bb6409a
--- /dev/null
+++ b/example/scenarios/mod-srsue-ncarriers@.conf
@@ -0,0 +1,3 @@
+modifiers:
+  modem:
+  - num_carriers: ${param1}