Draft: Implement initial functionality

This implements initial functionality to use QMI modem(s) as wireless WAN.

Only one modem at the time acting as WAN is currently supported. The expected setup is just one modem - i.e. Turris router with LTE kit - but code can handle multiple attached modems.

In that scenario all detected modems are offered as a choice, but there can be only one selected and designated as WAN.

Following API functions are currently implemented:

• get_settings
• update_settings

This MR depends on functionality implemented in: foris-controller!125

foris_controller_backends/wwan/__init__.py

@@ -100,7 +100,7 @@ class WWanUci:
         else:
             extra_auth = {"auth_type": "none"}
 
-        enabled = WWanUci._is_designated_as_wan(if_name)
+        enabled = NetworksUci.is_designated_as_wan(if_name)
 
         return {
             "id": dev_no,
@@ -181,16 +181,6 @@ class WWanUci:
 
         return int(match.group(1))
 
-    @staticmethod
-    def _is_designated_as_wan(if_name: str) -> bool:
-        """Check whether given interface is designated as WAN."""
-        wan_interfaces = NetworksUci.get_active_wan_interfaces()
-        if not wan_interfaces:
-            return False
-
-        # NOTE: is set really needed here?
-        return set(wan_interfaces) == {if_name}
-
 
 class WWanCmd(BaseCmdLine):
     @staticmethod