Fix network inspect compat API discrepancy

- containerInspect compat API expects field value PrefixLen
  instead of PrefixLength for type Address for SecondaryIPAddresses
- Add tests for network part of containerInspect compat api

Closes: containers#14674
Signed-off-by: 🤓 Mostafa Emami <mustafaemami@gmail.com>

test/apiv2/python/rest_api/fixtures/api_testcase.py

@@ -64,6 +64,10 @@ class APITestCase(unittest.TestCase):
     def uri(path):
         return APITestCase.PODMAN_URL + "/v2.0.0/libpod" + path
 
+    @staticmethod
+    def compat_uri(path):
+        return APITestCase.PODMAN_URL + "/v3.0.0/" + path
+
     def resolve_container(self, path):
         """Find 'first' container and return 'Id' formatted into given URI path."""