esp32: Add support for espnow based pktradio

Espnow is a connectionless WiFi communication protocol that can be used
to exchange information between esp nodes.

A espnow pktradio driver is proposed that allows building a 6lowpan
network of nodes.

The driver has been evaluated using udpclient & server running on
different devices.

Solves #15347

Signed-off-by: Laczen JMS <laczenjms@gmail.com>

boards/xtensa/esp32/esp32-devkitc/src/esp32_bringup.c

@@ -179,6 +179,10 @@
 #  include "espressif/esp_nxdiag.h"
 #endif
 
+#ifdef CONFIG_ESP32_ESPNOW_PKTRADIO
+#  include "esp32_espnow_pktradio.h"
+#endif
+
 #include "esp32-devkitc.h"
 
 /****************************************************************************
@@ -362,6 +366,15 @@ int esp32_bringup(void)
     }
 #endif
 
+#ifdef CONFIG_ESP32_ESPNOW_PKTRADIO
+  ret = pktradio_espnow();
+  if (ret < 0)
+    {
+      syslog(LOG_ERR, "ERROR: Failed to initialize ESPNOW pktradio=%d\n",
+             ret);
+    }
+#endif
+
 #ifdef CONFIG_ESP32_OPENETH
   ret = esp_openeth_initialize();
   if (ret < 0)