sysutils/hammer2: New port: HAMMER2 file system for FreeBSD

HAMMER2 file system for FreeBSD (read-only support).
https://gitweb.dragonflybsd.org/dragonfly.git/blob/HEAD:/sys/vfs/hammer2/DESIGN

Consists of hammer2.ko kernel module and sbin/* binaries.

WWW: https://github.com/kusumi/freebsd_hammer2

PR: 267982
Tested by: meta