Fix #26918: IOS TypeError (#26999)

Fix IOS TypeError

* if flags are None, then ' '.join(flags) fails
* fixed get_defaults_flag so that it returns a list, and ignores lines with white space

Fixes #26918

lib/ansible/module_utils/ios.py

@@ -71,13 +71,13 @@ def get_defaults_flag(module):
 
     commands = set()
     for line in out.splitlines():
-        if line:
+        if line.strip():
             commands.add(line.strip().split()[0])
 
     if 'all' in commands:
-        return 'all'
+        return ['all']
     else:
-        return 'full'
+        return ['full']
 
 
 def get_config(module, flags=[]):