cangen: make FD/XL content configurable in mixed mode

[hartkopp]

Suggested-by: Vincent Mailhol [email protected]

[marckleinebudde]

Let's discuss you approach in #599

[marckleinebudde]

Cc: @vincent-mailhol

[vincent-mailhol]

```c if (mix && (!canfd_en && !canxl_en)) { printf("-f and/or -X is required for -m (mixed mode)!\n"); return 1; } ``` This is not what I intended in my initial patch. The goal was to have the cangen automagically handle the logic for me so that I do not have to think about what flag to pass and this regardless of the interface capabilities. This actually goes in the opposite direction as I would now not be able to use -m alone. When testing, I use the cangen -m a lot an I always have this little frustration when getting the error message when the interface only support Classical CAN.

[marckleinebudde]

IMHO having the mixed mode doing the maximum mixing of the supported interface's capabilities is a good idea.

[hartkopp]

Ok, got it. Will prepare another patch.

[hartkopp]

Hey all,

I force pushed the patch on my master branch and did not realize that this automatically changed this pull request.
Then I removed the patch which closed this PR m(
So I now created a proper branch and opened a new PR for it.
Sorry for the noise.

[marckleinebudde]

FTR: new PR: #601