[JPLeRouzic]

As mangix said, it is not a question of "having this version in router's kernel" because it depends strictly on the kind of chip the hardware uses. Most Wi-Fi chips use their own program which is called "a binary blob", they do not use the Wi-Fi stack of Linux except as a wrapper around their own code, which is not accessible in source, only in binary.

This is why for example in Ubuntu (but also in most other Linux distributions) there are "third party codes" that are "not free".