packages: dhclient, local-unbound require resolvconf

Both of these packages use resolvconf for various things. Add a
dependency to make this work.

MFC after: 3 days
Reviewed by: des
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D53115

(cherry picked from commit bf28c98f14b439796b395eb4bf9070e4f7cffd68)