dhcp: Update to 4.4.1

dhcp: Update to 4.4.1

For details see:
https://kb.isc.org/article/AA-01571/82/DHCP-4.4.1-Release-Notes.html

This should close https://bugzilla.ipfire.org/show_bug.cgi?id=11697 and
https://bugzilla.ipfire.org/show_bug.cgi?id=11293.

This update required some changes as described in:
https://bugzilla.ipfire.org/show_bug.cgi?id=11697#c6

Thanks to all testers! ;-)

Best,
Matthias

Signed-off-by: Matthias Fischer <matthias.fischer@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>