The same issue exists when using the broadcom-sta-dkms package instead of bcmwl-kernel-source on kernel 4.4.0-21 (also as with bcmwl-kernel-source this packages works on kernel-4.4.0-18):
The loading of the module fails with modprobe: ERROR: could not insert 'wl': Required key not available. The reason seems to be because of insufficient privileges for some underlying action.
The same issue exists when using the broadcom-sta-dkms package instead of bcmwl-kernel-source on kernel 4.4.0-21 (also as with bcmwl-kernel-source this packages works on kernel-4.4.0-18):
The loading of the module fails with modprobe: ERROR: could not insert 'wl': Required key not available. The reason seems to be because of insufficient privileges for some underlying action.