Bluetooth: GATT: Writing 1 byte to a CCC access invalid memory

[Vudentz]

According to the spec it is valid to write less than attribute length:

BLUETOOTH CORE SPECIFICATION Version 5.1 | Vol 3, Part F
page 2320:

'If the attribute value has a fixed length and the Attribute Value
parameter length is less than or equal to the length of the attribute
value, the octets of the attribute value parameter length shall be
written; all other octets in this attribute value shall be
unchanged.'

So when writting just 1 byte to a CCC that would cause accessing invalid memory:

[00:02:13.530,000] bt_gatt.bt_gatt_attr_write_ccc: handle 0x0015 value 16385
[00:02:13.530,000] bt_gatt.gatt_ccc_changed: ccc 0x001510a4 value 0x4001