[nrf fromtree] bluetooth: host: downstream bluetooth/buf.h API change

doc/releases/migration-guide-4.1.rst

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+:orphan:
+
+.. _migration_4.1:
+
+Migration guide to Zephyr v4.1.0 (Working Draft)
+################################################
+
+This document describes the changes required when migrating your application from Zephyr v4.0.0 to
+Zephyr v4.1.0.
+
+Any other changes (not directly related to migrating applications) can be found in
+the :ref:`release notes<zephyr_4.1>`.
+
+.. contents::
+    :local:
+    :depth: 2
+
+Build System
+************
+
+Kernel
+******
+
+Boards
+******
+
+Modules
+*******
+
+Mbed TLS
+========
+
+Trusted Firmware-M
+==================
+
+LVGL
+====
+
+Device Drivers and Devicetree
+*****************************
+
+Controller Area Network (CAN)
+=============================
+
+Display
+=======
+
+Enhanced Serial Peripheral Interface (eSPI)
+===========================================
+
+GNSS
+====
+
+Input
+=====
+
+Interrupt Controller
+====================
+
+LED Strip
+=========
+
+Sensors
+=======
+
+Serial
+======
+
+Regulator
+=========
+
+Bluetooth
+*********
+
+Bluetooth HCI
+=============
+
+Bluetooth Mesh
+==============
+
+Bluetooth Audio
+===============
+
+Bluetooth Classic
+=================
+
+Bluetooth Host
+==============
+
+* :kconfig:option:`CONFIG_BT_BUF_ACL_RX_COUNT` has been deprecated. The number of ACL RX buffers is
+  now computed internally and is equal to :kconfig:option:`CONFIG_BT_MAX_CONN` + 1. If an application
+  needs more buffers, it can use the new :kconfig:option:`CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA` to add
+  additional ones.
+
+  e.g. if :kconfig:option:`CONFIG_BT_MAX_CONN` was ``3`` and
+  :kconfig:option:`CONFIG_BT_BUF_ACL_RX_COUNT` was ``7`` then
+  :kconfig:option:`CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA` should be set to ``7 - (3 + 1) = 3``.
+
+  .. warning::
+
+   The default value of :kconfig:option:`CONFIG_BT_BUF_ACL_RX_COUNT` has been set to 0.
+
+Bluetooth Crypto
+================
+
+Networking
+**********
+
+Other Subsystems
+****************
+
+Flash map
+=========
+
+hawkBit
+=======
+
+MCUmgr
+======
+
+Modem
+=====
+
+Architectures
+*************