add IPv6 default route interface auto-detection for permanent/temporary IPv6 without netif

- get_default_route_netif_index(): UDP connect trick + getifaddrs to find default route iface
- etcp_socket_add(): auto-detect netif_index when not specified in config
- queue_new() API: explicit index_offset/index_size params instead of implicit from hash_size
- radix: cleanup types (uint8_t*), replace bzero/bcmp with memset/memcmp, remove kernel ifdefs
- route6_lib: new IPv6 routing library + get_node_v6_routes()

.gitignore

@@ -92,6 +92,12 @@ utun.conf
 tools/bping/bping
 tools/proxy/udp_proxy
 
+# Debug/temp artifacts
+*.bak
+*.debug
+*.csv
+__pycache__/
+
 
 # MSVC temp files
 cl