Commit for ticket #5755, issue ascom-au/ensurespeech-playbook#10

tasks/dahdi.yml
* Added task which modifies the drivers/dahdi/firmware/Makefile to allow
offline downloading of any firware source packages
* Added task which copies the dahdi-fwload-vpmadt032-1.25.0.tar.gz source
packages into the /tmp folder to allow offline installation

files/dahdi-fwload-vpmadt032-1.25.0.tar.gz
* Added echo canceler source package to allow offline installation