net-mgmt/nfs-exporter: update to 0.3.2

This version fixes a crash that can happen on a busy server with high
uptime. It also runs as an unprivileged user on FreeBSD 14.

Sponsored by: Axcient
Reviewed by: otis
Approved by: otis (ports)
Differential Revision: https://reviews.freebsd.org/D37655