Add support for openwrt packages

[pombredanne]

Short Description

These are highly similar to Debian package as they based on .deb
They use the same layout and control files, but no copyright files. Instead they use for short license code for licenses

See https://downloads.openwrt.org/ for examples ... for instance https://archive.openwrt.org/releases/18.06.0/targets/ipq806x/generic/packages/

[chinyeungli]

For /baseline/ipq/gdb_7.8-2_ipq.ipk
I've package__declared_license as "GPL-3.0+" , but package__license_expression as "gpl-2.0-plus"
Perhaps this is a bug?

[pombredanne]

For /baseline/ipq/gdb_7.8-2_ipq.ipk
I've package__declared_license as "GPL-3.0+" , but package__license_expression as "gpl-2.0-plus"
Perhaps this is a bug?

That's a bug alright! good catch! the bug is here: https://github.com/nexB/scancode-toolkit/blob/0d2ac9ca4901a5e6ff903b08f94bf8ec21fb3d44/src/packagedcode/openwrt.py#L407