Introduce CFINCOMPATIBLE config parse result flag.
Sort interface rules by unsigned integer key.
Legacy and modern 'interfaces' config styles are now incompatible.
Validate config_network_interface struct to enforce that only exactly one of
'match' and 'dummy' options are set.
Add test cases for 'interface' config option.
Change a test case: configuration options are now case sensitive.
Fix config file load and parse logic in conf.c, always copy 'debug' flags
from config.debug.
The config schema 'interfaces' option is no longer MANDATORY.
Introduce new CLIFLAG_PERMISSIVE_CONFIG to supress bad-config ERROR messages
from the 'config set' and 'config get' commands.
Refactor cli_execute() into cli_parse() and cli_invoke(). Use *const* struct
command_line_option everywhere.
