please add backport-iwlwifi-dkms to the dkms package set

[Andrea Righi]

backport-iwlwifi-dkms provides the backported iwlwifi driver.

This module should be considered deprecated with recent kernels, but we
still need to support it for the certified laptops that cannot use the
stock iwlwifi.

The package provides kernel modules that are installed and built like
any other dkms, so it should be considered part of the dkms group.

Thanks,
-Andrea