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/src/osmo_gsm_tester/resource.py b/src/osmo_gsm_tester/resource.py
index 3b805ff..bb44f39 100644
--- a/src/osmo_gsm_tester/resource.py
+++ b/src/osmo_gsm_tester/resource.py
@@ -108,6 +108,7 @@
         'modem[].features[]': schema.MODEM_FEATURE,
         'modem[].rf_dev_type': schema.STR,
         'modem[].rf_dev_args': schema.STR,
+        'modem[].num_carriers': schema.STR,
         'modem[].airplane_t_on_ms': schema.INT,
         'modem[].airplane_t_off_ms': schema.INT,
         'osmocon_phone[].serial_device': schema.STR,