Setting static ip without netmask causes a reboot loop

[Olverine]

The issue

If a static ip is set without static netmask, the device will reboot endlessly.

The following log messages are printed over and over:

mgos_freertos.c:157     Mongoose OS 2.20.0 (20221020-084933/2.20.0-g1885c0f)
mgos_freertos.c:161     CPU: 160 MHz, FreeRTOS 8.2.0, heap: 286352 total, 254164 free
mgos_freertos.c:163     Newlib 3.0.0
esp32_main.c:65         ESP-IDF 4.2-r8
esp32_main.c:68         Boot partition: app_1; flash: 4M
mongoose.c:15766        Mongoose 6.18, LwIP 2.1.3
mongoose.c:4932         mbed TLS 2.16.11-cesanta1
mgos_vfs_dev.c:73       nvs: esp32part ({"label": "nvs"}), size 16384
mgos_vfs_dev.c:73       otadata: esp32part ({"label": "otadata"}), size 8192
mgos_vfs_dev.c:73       fs_0: esp32part ({"label": "fs_0"}), size 262144
mgos_vfs_dev.c:73       fs_1: esp32part ({"label": "fs_1"}), size 262144
mgos_vfs.c:174          /: SPIFFS @ fs_1, opts {"bs":4096,"ps":256,"es":4096}
mgos_vfs.c:347          /: size 233681, used: 94627, free: 139054
mgos_sys_config.c:470   MAC: e8:9f:6d:d2:3c:44
mgos_sys_config.c:478   WDT: 30 seconds
mgos_ota_shadow_lib:116 OTA over shadow initialised
I (1438) esp_eth.netif.glue: e8:9f:6d:d2:3c:47
I (1448) esp_eth.netif.glue: ethernet attached to netif
mgos_eth.c:109          Invalid eth.netmask!
mgos_deps_init.c:320    ethernet init failed
mgos_freertos.c:184     MGOS init failed: -32
mgos_vfs.c:1026         Unmounting filesystems
mgos_system.c:43        Restarting

How to replicate

1. Send rpc request to set a static ip without a static netmask
2. Send rpc request to save configuration
3. Reboot device

Expected behavior

It would be reasonable to expect the same behavior that you get when following the exact same steps but set a static wifi ip instead.
On step two, you would get the following response (from a http rpc request with status code 500)

Instead, you get the following (with http status 200) when setting the ip for ethernet.