Fix RAM corruption caused by our hook of register_chipv6_phy(init_data*).

"init_data", when non-NULL, is on the heap, and the register_chipv6_phy call
sometimes modifies data in (at least) the offset range [128:249], suggesting
that it is a buffer larger than 128 bytes in size (the size of our
"phy_init_data" buffer).  When we use our static buffer (prior to this
change), the call could would overwrite the .rodata section and lead to
undefined behaviour.

To address this, just patch the heap-allocated buffer with our data.

Move phy_init_data to flash as it's now readonly and never modified.

Author: alltheblinkythings

cores/esp8266/core_esp8266_phy.c

@@ -24,7 +24,9 @@
  #include <stddef.h>
  #include <stdbool.h>
 
-static uint8_t phy_init_data[128] =
+#include "c_types.h"
+
+static const uint8_t ICACHE_FLASH_ATTR phy_init_data[128] =
 {
     [0] = 5,  // Reserved, do not change
     [1] = 0,  // Reserved, do not change
@@ -241,9 +243,12 @@ static uint8_t phy_init_data[128] =
 };
 
 extern int __real_register_chipv6_phy(uint8_t* init_data);
-extern int __wrap_register_chipv6_phy(uint8_t* unused) {
-    phy_init_data[107] = __get_adc_mode();
-    return __real_register_chipv6_phy(phy_init_data);
+extern int __wrap_register_chipv6_phy(uint8_t* init_data) {
+    if (init_data != NULL) {
+      memcpy(init_data, phy_init_data, sizeof(phy_init_data));
+      init_data[107] = __get_adc_mode();
+    }
+    return __real_register_chipv6_phy(init_data);
 }
 
 extern int __get_rf_mode(void)  __attribute__((weak));