fixes an issue with dict_merge in network utils (#41107)

This change address a problem where the dict_merge function would fail
due to the value being a nested dict.  This will now recursively pass
the value back through the dict_merge function.
Merge to devel https://github.com/ansible/ansible/pull/41107

(cherry picked from commit 2a4be2748f)

Update changelog

Fix review comments

changelogs/fragments/49474-network_utils_dict_merge_fix.yaml

@@ -0,0 +1,3 @@
+---
+bugfixes:
+- fixes an issue with dict_merge in network utils (https://github.com/ansible/ansible/pull/49474)

lib/ansible/module_utils/network/common/utils.py

@@ -34,6 +34,7 @@ from itertools import chain
 from struct import pack
 from socket import inet_aton, inet_ntoa
 
+from ansible.module_utils.common._collections_compat import Mapping
 from ansible.module_utils.six import iteritems, string_types
 from ansible.module_utils.six.moves import zip
 from ansible.module_utils.basic import AnsibleFallbackNotFound
@@ -275,7 +276,10 @@ def dict_merge(base, other):
             if key in other:
                 item = other.get(key)
                 if item is not None:
-                    combined[key] = dict_merge(value, other[key])
+                    if isinstance(other[key], Mapping):
+                        combined[key] = dict_merge(value, other[key])
+                    else:
+                        combined[key] = other[key]
                 else:
                     combined[key] = item
             else: