Fix Tunnel Virtual Network params:

[vavsab]

Description

1. Fix misspelled vnet param
2. Make default network param required

Docs are misleading.

1. vnet_name is actually name
   
   
2. is_default is actually required during creation
   

Has your change been tested?

Covered with unit tests

Screenshots (if appropriate):

Types of changes

What sort of change does your code introduce/modify?

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• This change is using publicly documented (api.cloudflare.com or developers.cloudflare.com) and stable APIs.

#913
cloudflare/terraform-provider-cloudflare#1602

[jacobbednarz]

thanks, i'll mention to the team the public docs are incorrect.