Allow check_mode with supports_generate_diff capability in cli_config (#51384)

* If network cliconf support `supports_generate_diff` in
  that case diff between running and cnadidate config
  is generated within Ansible and if check_mode is enabled
  in that case return only diff without actually invoking
  edit_config()

(cherry picked from commit 8f5cd049d6)

changelogs/fragments/cli_config_diff_fix.yaml

@@ -0,0 +1,3 @@
+---
+minor_changes:
+  - Allow check_mode with supports_generate_diff capability in cli_config. (https://github.com/ansible/ansible/pull/51417)

lib/ansible/modules/network/cli/cli_config.py

@@ -251,7 +251,8 @@ def run(module, capabilities, connection, candidate, running):
 
             kwargs = {'candidate': candidate, 'commit': commit, 'replace': replace,
                       'comment': commit_comment}
-            connection.edit_config(**kwargs)
+            if commit:
+                connection.edit_config(**kwargs)
             result['changed'] = True
 
         if banner_diff:
@@ -260,7 +261,8 @@ def run(module, capabilities, connection, candidate, running):
             kwargs = {'candidate': candidate, 'commit': commit}
             if multiline_delimiter:
                 kwargs.update({'multiline_delimiter': multiline_delimiter})
-            connection.edit_banner(**kwargs)
+            if commit:
+                connection.edit_banner(**kwargs)
             result['changed'] = True
 
     if module._diff: