NimBLE: Add error prints for ACL buffer exhaustion in NPL

components/bt/host/nimble/esp-hci/src/esp_nimble_hci.c

@@ -252,6 +252,7 @@ static struct os_mbuf *ble_hci_trans_acl_buf_alloc(void)
 static void ble_hci_rx_acl(uint8_t *data, uint16_t len)
 {
     struct os_mbuf *m;
+    int rc;
     int sr;
     if (len < BLE_HCI_DATA_HDR_SZ || len > MYNEWT_VAL(BLE_ACL_BUF_SIZE)) {
         return;
@@ -260,9 +261,11 @@ static void ble_hci_rx_acl(uint8_t *data, uint16_t len)
     m = ble_hci_trans_acl_buf_alloc();
 
     if (!m) {
+        ESP_LOGE(TAG, "%s failed to allocate ACL buffers; increase ACL_BUF_COUNT", __func__);
         return;
     }
-    if (os_mbuf_append(m, data, len)) {
+    if ((rc = os_mbuf_append(m, data, len)) != 0) {
+        ESP_LOGE(TAG, "%s failed to os_mbuf_append; rc = %d", __func__, rc);
         os_mbuf_free_chain(m);
         return;
     }