When you reboot linux, watch the kernel log and see if you can see brcm. it should be close to the end of it's onscreen log before switch over to lxde.
If it is there, you might have to try manually starting the driver using modprobe. I'm not sure which it is using though. brcmsmac, b43, bcma (comma separated) are ones i can think of. I dont have the stuff to boot linux up right now to check everything unfortunately.
This shouldn't be required though, I think it is built into the kernel. Did you compile the kernel yourself? Try using this repository if you aren't already for starting the exploit and running linux. Everything was prepared.
And just to be clear, rebooting means hitting reboot in the power menu or using reboot in the console. Shutdown and reboot does not work. Power must remain on. Not being condescending, just being clear.
https://github.com/SoulCipher/shofel2_linux