I found some workaround for this problem from
https://bugs.launchpad.net/ubuntu/+source/dahdi-linux/+bug/1703711:
Add these lines to /usr/src/dahdi-2.11.1.0.20170917~dfsg-5/dkms.conf:
BUILT_MODULE_NAME[32]="oct612x"
BUILT_MODULE_LOCATION[32]="drivers/dahdi/oct612x/"
DEST_MODULE_LOCATION[32]="/kernel/drivers/telephony/dahdi"
and rebuild/reinstall modules:
# dkms build dahdi/2.11.1.0.20170917~dfsg-5
# dkms install dahdi/2.11.1.0.20170917~dfsg-5
p.s. Also had to correct the scripts in /usr/sbin/dahdi* changing
$device/spantype to $device/dahdi_spantype:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=916577
