gap: store link key for standard/non-SSP pairing

# Conflicts:
# CHANGELOG.md

hci: fix signed warning

hci: remove redundant check

hci: add hci_get_stack for testing

hci: use assert in hci_number_free_acl_slots_for_connection_type

hci: update state before sending hci command

hci: fix warnings

hci: fix cis to iso stream assignment in central role

hci: fix emit cis/bis created

hci: send hci_le_set_host_feature only if supported

hci: use correct guards for hci_handle_connection_failed

hci: use correct guards for le_handle_extended_advertisement_report and hci_le_num_phys

Analog to PR #642

hci: truncate L2CAP packet to l2cap PDU size

gap: add gap_request_connection_subrating

hci: enable connection subrating during init

hci: fix caching of authentication requirements used in hci io capability request reply

gap: only store link key if at least one side requests bonding during the IO Capabilities exchange.

hci: store ssp io capability request reply auth requirements in connection

hci: fix log level

hci: use null address as placeholder for announced connections

hci: improve handling of advertising set terminated for legacy advertising api

hci: introduce LE_EXTENDED_ADVERTISING_LEGACY_HANDLE

hci: fix detection for HCI_COMMAND_LE_SET_EXTENDED_ADVERTISING_ENABLE

hci: fix typo

hci: skip failed cis during iso path setup