le_device_db: add secure connection field

hci: only pause during halting if hci_halting_defer is called after receiving BTSTACK_EVENT_STATE

hci: pause 500 ms during halting

hci: track outgoing / received SCO bytes to calculate num SCO slots used in controller

hci: unify num_acl_packets_sent + num_sco_packets_sent into single num_packets_sent in hci_connection_t

hci: release outgoing buffer on disconnect if waiting to send another ACL fragment

gap: add gap_le_set_phy command

hci: check if LE Set Defaut PHY is supported

hci/gap: save the le connection interval on connection complete and connection update

hci/gap: support snif mode

hci: track connection mode

gap: add gap_set_default_link_policy_settings

hci: free hci connection struct on error reported in hci command status event

hci: return -1 if hci_create_connection was not sent to transport layer in hci_send_cmd_packet

att: ENABLE_ATT_DELAYED_READ_RESPONSE -> ENABLE_ATT_DELAYED_RESPONSE, example/att_delayed_read_response.c -> example/att_delayed_response.c

Replaced HCI_PACKET_BUFFER_SIZE with HCI_INCOMING_PACKET_BUFFER_SIZE and HCI_OUTGOING_PACKET_BUFFER_SIZE

hci: avoid anonymous union

att_server: add att_server_request_to_send_notification and att_server_request_to_send_indication

hci: allow HCI_OUTGOING_PRE_BUFFER_SIZE to be overridden in btstack_config.h

Merge branch 'develop-crypto' into develop

gap: handle HCI_SUBEVENT_LE_REMOTE_CONNECTION_PARAMETER_REQUEST

sm: drop unused states

sm: rename sm_boding_requested to sm_pairing_requested

att: support for delayed att read response

GAP: allow to limit number of connections in LE Peripheral role with gap_set_max_number_peripheral_connections