extmod/nimble/modbluetooth_nimble: Handle port init failures.

This commit fixes an issue related to the NimBLE initialisation
procedure in low memory environments on ESP32 boards.

MicroPython uses at least two different NimBLE stacks across the
supported ports, mynewt (imported as an external library), and the one
provided by Espressif in their own SDKs.  The problem is that these two
ports differ in the signature for `nimble_port_init(void)`, with mynewt
returning `void`, and Espressif's returning a status code on failure.

On ESP32 boards, allocating almost all the available heap and then
turning on the Bluetooth stack would trigger a failure in the NimBLE
initialisation function that is not handled by the NimBLE integration
code, as there's no expectation of a recoverable condition.  Since the
stack initialisation would progress, then uninitialised memory accesses
crash the board.

Since we cannot really modify neither mynewt nor Espressif SDKs, the
next best thing is to provide two conditional initialisation paths
depending on a configuration setting.  This would make Espressif ports
recover from a failed initialisation whilst retaining the existing
behaviour on other ports.

This fixes micropython#14293.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>

Author: agatti

extmod/nimble/modbluetooth_nimble.c

@@ -618,7 +618,17 @@ int mp_bluetooth_init(void) {
 
     // Initialise NimBLE memory and data structures.
     DEBUG_printf("mp_bluetooth_init: nimble_port_init\n");
+
+    // On some ports `nimble_port_init` may return an error code indicating a
+    // failed initialisation.
+    #if MICROPY_BLUETOOTH_NIMBLE_PORT_INIT_RETURNS_ERROR
+    if (nimble_port_init() < 0) {
+        mp_bluetooth_deinit();
+        return MP_EIO;
+    }
+    #else
     nimble_port_init();
+    #endif
 
     ble_hs_cfg.reset_cb = reset_cb;
     ble_hs_cfg.sync_cb = sync_cb;

ports/esp32/mpconfigport.h

@@ -108,6 +108,7 @@
 #define MICROPY_PY_BLUETOOTH_ENABLE_PAIRING_BONDING (1)
 #define MICROPY_BLUETOOTH_NIMBLE            (1)
 #define MICROPY_BLUETOOTH_NIMBLE_BINDINGS_ONLY (1)
+#define MICROPY_BLUETOOTH_NIMBLE_PORT_INIT_RETURNS_ERROR (1)
 #endif // MICROPY_PY_BLUETOOTH
 
 #define MICROPY_PY_RANDOM_SEED_INIT_FUNC    (esp_random())