Generated .net v3.5 client fails to compile with error "Default parameter specifiers are not permitted"

Description

I tried to generate csharp .net v3.5 client for the default .net core webapi template and it fails to compile.

I get multiple errors like following when trying to compile a client.

src\IO.Swagger\Client\Configuration.cs(133,29): error CS0241: Default parameter specifiers are not permitted

Swagger-codegen version

cloned with this commit https://github.com/swagger-api/swagger-codegen/commit/8067612e06172942c5d661f0988bb866492d1cab

Swagger declaration file content or url

https://gist.github.com/PoisonousJohn/41da6885eac2a2cbfc60304faf7ab88b

Command line used for generation

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate \
>    -i http://localhost:5000/swagger/v1/swagger.json \
>    -l csharp -DtargetFramework=v3.5 \
>    -o ~/projects/csharpApiClient

Steps to reproduce

1. launch swagger generation
2. run ./build.bat to build a client dll
3. notice errors

Related issues/PRs

Suggest a fix/enhancement

remove default values from method parameters in favor of overloads without additional arguments

Start with the generated Client/Configuration.cs at the reported line and reproduce the failure using the Java generation command with -l csharp and -DtargetFramework=v3.5. Run ./build.bat and inspect the generated method parameters; done means the generated client compiles without CS0241 errors for the provided Swagger declaration.