It clashes with openvpn_client module when both
openvpn and openwpn_client modules are installed from a single
requirements.txt file.

Change "option ifname" to "option device"

See: https://openwrt.org/releases/21.02/notes-21.02.0#new_network_configuration_syntax_and_boardjson_change

Temporary workaround for deprecated integration with setuptools since
version >=4.0

Useful in case when configuration is derived from other uci configs (e.g.
networks) and we want to be able to trigger update of openvpn config

The link_dh is new command that allows linking pre-generated dhparam
file instead of generating new one.
There is still an option to generate new one and of course previous one
is not touched. This applies only for new certificates.
There should be no issue in using pre-generated dhparam and at the same
time is is huge time saver.

Default topology net30 is deprecated and for legacy clients only (year 2014).
By using the topology subnet directive, it makes the routing table easier to read and simplifies the routing.

This changes how dhparam is generated. Until now separate script and
package was used to generate dhparam while turris-cagen is able to do
the same.

This is simple change and allows us to remove one dependency. It takes
some time to generate CA and generating dhparam as part of that makes
sense as well. It is true that it prolongs initial generation (and that
was probably original reason why moving it to separate package) but
this way it is more consistent. It is generated only by user and all is
stored in same location.

Existing configuration is going to be migrated by fix package. That
means missing dhparam is going to be generated and configuration updated
with openvpn reload after that.

* no compression is set by default
* get_client_config is able to process 'comp_lzo' uci option
* get_client_config generates config with '' or 'compress <alg>'

setup.py: test dependencies updated (ubus and paho-mqtt are not mandatory modules for foris-controller)