It doesn’t; FreeBSD’s Linux compatibility layer does not run under our FreeBSD compatibility layer, and there are not any WiFi drivers that use this feature in FreeBSD anyway.
The BCM4313 is supported by a native FreeBSD driver, not a Linux-ported one. The reason I haven’t attempted porting it to our FreeBSD layer is its use of some weird Broadcom-specific busses that will be a pain to get wired into our compatibility layer correctly.
At this point, I’m pretty close to abandoning this approach; FreeBSD’s code here is just a huge mess and not worth that effort. I’m looking at OpenBSD’s drivers instead.
This is also not true. For the most performance-critical functions, most of the wrapping is inlined indeed; but there are still wrapper functions which would be wrappers of wrappers.
There are actually some FreeBSD network drivers dependent on the Linux compatibility layer (some strange 10Gb Ethernet drivers, not anything WiFi related, but still.)