Fix os_router ignores enable_snat: no (#45921)

If enable_snat is False, this should be used to build the
request, because the default value in the OpenStack Networking
API is True.

Fixes the issue #45915.

(cherry picked from commit 452a4ab781)

changelogs/fragments/45921-os_router-ignores-enable_snat-no.yml

@@ -0,0 +1,2 @@
+bugfixes:
+    - "os_router - ``enable_snat: no`` was ignored."

lib/ansible/modules/cloud/openstack/os_router.py

@@ -306,7 +306,7 @@ def _build_kwargs(cloud, module, router, network):
     if network:
         kwargs['ext_gateway_net_id'] = network['id']
         # can't send enable_snat unless we have a network
-        if module.params['enable_snat']:
+        if module.params.get('enable_snat') is not None:
             kwargs['enable_snat'] = module.params['enable_snat']
 
     if module.params['external_fixed_ips']: