man5/{hosts,resolver}.5: note that IPv6 addresses are allowed.

The patch in the PR largely no longer applied due to age, but
thanks to Evgeniy Khramtsov for the patches in the PR.

PR: 120024
Reported by: bcran
Approved by: blackend (mentor)
Obtained from: Evgeniy Khramtsov <evgeniy@khramtsov.org> (partly)