Replace inline definitions with shared functions: log, has_option,
rule_pref, resolve_gw, resolve_default_gw. Use read_value/read_values
instead of grep -v '^#' | grep -m1, ipcmd_for instead of manual
detection, table_by_name inside lookup_table.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>