Fix overwrite parameter in module_utils.junos (#18671)

The overwrite parameter is forcibly set to false, meaning a module
passing that parameter will have no effect.  The overwrite facility
is necessary to ensure that conflicting options can be written the
configuration (which, in replace mode, they cannot).

This change ensures that if overwrite is set, it will not be changed
to False in the logic.
(cherry picked from commit 9e5d4de49a)

lib/ansible/module_utils/junos.py

@@ -184,8 +184,8 @@ class Netconf(object):
             merge = False
             overwrite = False
         elif overwrite:
-            merge = True
-            overwrite = False
+            merge = False
+            overwrite = True
         else:
             merge = True
             overwrite = False