datamodel: support interface names with dashes

Dashes can't be present in normal identifiers in Lua, so we switch to a different syntactic sugar for the same thing.

Fixes #900 (closed)

manager/knot_resolver_manager/datamodel/templates/macros/network_macros.lua.j2

@@ -31,7 +31,7 @@ net.listen(
 {%- if interface.addr -%}
 '{{ interface.addr }}',
 {%- elif interface.if_name -%}
-net.{{ interface.if_name }},
+net['{{ interface.if_name }}'],
 {%- endif -%}
 {%- if interface.port -%}
 {{ interface.port }},