package/radvd: bump version to 2.20
Radvd now uses libbsd.
Changelog:
https://github.com/radvd-project/radvd/blob/v2.20/CHANGES
Signed-off-by: Akhilesh Nema <nemaakhilesh@gmail.com>
[Peter: add and propagate remaining libbsd dependencies]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>