Update to 4.4.2 and make it work @th-2020.

Update to 4.4.2 and make it work @th-2020.

- dropped dhclient-decline-backoff patch. The source has changed beyond any hope in the meantime. Also if I read the new source correctly, it supports the DECLINE messages itself.
- dropped dhclient_hooks_d.patch. The patch is not needed anymore, as the original code now uses "run-parts" tool, which is smart enough to avoid .rpmnew files and the likes.
- added a new patch (extravars) that fixes a build breakage caused by some variables declared multiple times. This seems to be broken in original unpatched distribution of dhcp. I assume we run into that issue because of some combination of compiler options we use.