Make code size limit to change on EWASMForkBlock

[axic]

Change the "code size limit" commit d8b738f to be enabled on the EWASMForkBlock.

[axic]

Implemented this on this branch: https://github.com/ewasm/go-ethereum/tree/ewasm-fork-block

[axic]

@gballet do you want to check the above branch?

[axic]

@gballet @chfast should we open a PR upstream with that branch?

[chfast]

I'll do that.