I just upgraded from Ubuntu 15 to Xenial and my wifi drivers in the new kernel version (4.4.0-21-generic) stopped to work.
I downloaded on a pen drive the following packages:
And installed them manually on the new kernel:
# First uninstalled the old stuff
sudo apt-get remove --purge bcmwl-kernel-source
sudo apt-get remove --purge dkms
# Installed the new packages
sudo dpkg -i dkms_184.108.40.206-2ubuntu11_all.deb
sudo dpkg -i bcmwl-kernel-source_220.127.116.11+bdcom-0ubuntu8_amd64.deb
During the installation of the drivers I got a weird error:
modprobe: ERROR: could not insert 'wl': Required key not available
Googling a little bit I found out that the problem is caused by the Secure Boot option in the BIOS:
Disabling that specific option the module started to work.