This is a quick and dirty trick to take control of this misbehaving network card.
Scripts are tested on Fedora 29. If you have any problems, please file an issue here on GitHub.
Note that I did not want to package this workaround because it's, well, dirty. It does not fix the problem, just makes things bearable.
# ./install.sh
Remember to blacklist the kernel module at system startup. Appending modprobe.blacklist=brcmfmac in GRUB config is sufficient.
# systemctl start broadcom
# systemctl stop broadcom
# systemctl restart broadcom
# systemctl stop broadcom
# systemctl disable broadcom
# rm /usr/local/bin/broadcomctl
# rm /etc/systemd/system/broadcom.service