vyos.configdict: T4391: enable get_interface_dict() ti be used with ConfigTreeQuery()

When VyOS is booting and an interface is brought up (PPPoE) which requires a
user callback script that is executed asynchronously when the interface is up
we can not use Config(). The problem is, Config() is not available when
the system starts and the initial commit is still processed.

We need to move to ConfigTreeQuery() which was build for this exact same
purpose. TO reduce side effects and also dependencies on the entire
vyos.configdict library the set_level()/get_level() calls got eliminated
from within the library. All calls to functions like:

• get_removed_vlans()
• is_node_changed()
• leaf_node_changed()
• is_mirror_intf()
• ...

Now require that the full config path to the node is passed.