dns/knot2: update 2.3.1 -> 2.3.2

• Disable recvmmsg by default, this impacted UDP queries on 11.0-RELEASE. It was later fixed in 11/stable in r307311 but enabling conditionally provides little benefit so just disable by default as part of update.

PR: 213952, 214303
Submitted by: Leo Vandewoestijne <freebsd@dns-lab.com> (maintainer)