Utilize reserved phy_init partition on ESP32 for wifi calibration data

The `phy_init` partition has been reserved, but not used. By using the `WIFI_STORAGE_FLASH` location
the calibration data is preserved across restarts in flash significantly improving connection
times. The data stored using `WIFI_STORAGE_RAM` is lost at boot up and needs to be recalibrated,
the option `WIFI_STORAGE_FLASH` will still load the data into ram from flash, but this is much
faster than performing a full calibration every boot, and should significantly help battery powered
devices that spend time in deep sleep and only wake to collect and relay sensor data to the network.

Signed-off-by: Winford <winford@object.stream>

Author: UncleGrumpy

CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - ESP32: improved sntp sync speed from a cold boot.
+- Utilize reserved `phy_init` partition on ESP32 to store wifi calibration for faster connections.
 
 ## [0.6.6] - Unreleased
 

src/platforms/esp32/components/avm_builtins/network_driver.c

@@ -690,7 +690,7 @@ static void start_network(Context *ctx, term pid, term ref, term config)
         port_send_reply(ctx, pid, ref, error);
         return;
     }
-    if (UNLIKELY((err = esp_wifi_set_storage(WIFI_STORAGE_RAM)) != ESP_OK)) {
+    if (UNLIKELY((err = esp_wifi_set_storage(WIFI_STORAGE_FLASH)) != ESP_OK)) {
         ESP_LOGE(TAG, "Failed to set ESP WiFi storage");
         term error = port_create_error_tuple(ctx, term_from_int(err));
         port_send_reply(ctx, pid, ref, error);