Also homogenize a little some parameters between the differents models.
There is still work to be done there.

Note that regarding the auto_provision.custom.protect parameter, not all
models supports it; all phones in version earlier than V73 do not. This
includes:

* T32G
* T38G
* T19P
* T21P

Deprecated by the 3.3.1-SP4 plugin.

Use the latest SP4 firmware (i.e. HF1/HF2). Note that this plugin has
never been pushed to stable yet.

Now that the 6800 series are supported by the 4.0.0 plugin, it's simpler
if the 3.3.1 plugin, which has never been pushed to stable, doesn't include
them.

This fix #5351.

This remove a useless warning saying that a model was not supported
altough it was.

But for BLFs, the supervision still doesn't work when using the failover
identity.

It supports the T4X phones, which are already supported by the newer
xivo-yealink-72.0 plugin.

A little bit.

Lines starting with a comma are not valid in the M7+M2 configuration
file. At least, the T38 is not updating its configuration when this line
is present.

Replaced/superseded by xivo-snom-8.7.5.13.