att: handle invalid requests & commands

att_db: allow ATT Read Callback to return custom ATT Error Code

use bool instead of int vars

MISRAC2012-Rule-14.4_c: compare against 0 or NULL

gatt_client/att_server: track mtu exchanged in hci_connection->att_connection

add missing default switch cases

att_db: use btstack_min

att_db: improve and test att_read_callback_handle_blob

att_db: exclude auto pts code from LOCV

att_db: remove commented TODO as it is handled

auto-pts: try mapping btstack security level to single read/write permission

auto-pts: track security level in att_connection struct, pass att_connection to btp_att_get_attribute_value

auto-pts: fix compile for regular projects

auto-pts: support BTP_GATT_OP_GET_ATTRIBUTES with UUID len = 0

auto-pts: more debug output for att_db

auto-pts: more debug output for att_db

att_db: add helper functions for auto-pts btpclient

MISRAC2012-Rule-10.4_a: append 'u' to constant literals when used in unsigned expressions or comparisons

att_db: skip att_read_callback for ATT Read Blob Request if offset == value_len

att_db: rework handle_read_by_type_request2

att_db: additionally limit echo to response buffer size for prepare write request

att_db: streamline size validation as att_copy_value already limits attribute value to provided buffer

att_db: use ATT_DEFAULT_MTU as minimum after MTU exchange

att_db: report write not permitted if no att write callback set

att_db: validate size for ATT_WRITE_REQUEST