If you try and specify them together you will get this error:
google_compute_global_forwarding_rule.your-rule: Error creating Global Forwarding Rule: googleapi: Error 400: Invalid value for field 'resource.ipVersion': 'IPV4'. Both IP Version and IP Address cannot be specified., invalid
* Add versioned Beta support to google_compute_global_forwarding_rule.
* Add Beta support for ip_version in google_compute_global_forwarding_rule.
* Temporary commit with compute_shared_operation.go changes.
* Added a test to see if v1 GFR is still IPV4, moved to a TestCheckFunc
* This API returns the original self links, but let's make sure we don't diff.