python/trx: rename 'change_sign_of_dict_elements' to 'dict_toggle_sign'

The old name was quite long, resulting into cumbersome imports:

  from change_sign_of_dict_elements import change_sign_of_dict_elements

let's use a shorter variant:

  from dict_toggle_sign import dict_toggle_sign

Change-Id: Ie75e1d6e5e74c7c1cf34154633c1472e4b85dbb6
diff --git a/python/trx/CMakeLists.txt b/python/trx/CMakeLists.txt
index c6e3010..ffe5234 100644
--- a/python/trx/CMakeLists.txt
+++ b/python/trx/CMakeLists.txt
@@ -26,6 +26,6 @@
     fake_pm.py
     radio_if.py
     radio_if_grc.py
-    change_sign_of_dict_elements.py
+    dict_toggle_sign.py
     DESTINATION ${GR_PYTHON_DIR}/grgsm/trx
 )