l2cap: avoid ENABLE_x defines for local flags

btstack_config: use official terms for l2cap channel modes - ENABLE_L2CAP_ENHANCED_CREDIT_BASED_FLOW_CONTROL_MODE

btstack_config: use official terms for l2cap channel modes - ENABLE_L2CAP_LE_CREDIT_BASED_FLOW_CONTROL_MODE

l2cap: fix compile with le credit-based flow-control mode and without classic

l2cap: support enhanced credit-based control-flow mode

# Conflicts:
# src/l2cap.c

l2cap: reserve local cid 0xffff

l2cap: emit L2CAP_EVENT_INFORMATION_RESPONSE

l2cap: fixed_channels_supported instead of fixed_channels

l2cap: trigger information request for outgoing connections only if ERTM requested

l2cap: trigger information request for incoming connections after connection was accepted by user

l2cap: send fixed channel request

l2cap: remove block around INFORMATION_RESPONSE case

l2cap: extract l2cap_handle_information_request_complete

l2cap: trigger information request on: encryption, in- and outgoing connections

l2cap: provide l2ap_run_information_requests

l2cap: eplaced l2cap_register_packet_handler with l2cap_add_event_handler to register multiple handlers

l2cap: ENABLE_EXPLICIT_BR_EDR_SECURITY_MANAGER reports support for BR/EDR SM in information response

license: update text

docs: use @return instead of @returns

l2cap: incoming SDP connection don't need remote features

l2cap: outgoing SDP connection don't need remote features

l2cap: hci_remote_features_query already called in l2cap_handle_connection_complete already for outgoing connections

l2cap: extract l2cap_send_signaling_packet usable for br/edr and le

l2cap: rename l2cap_send_signaling_packet into l2cap_classic_send_signaling_packet

l2cap: inline l2cap_create_signaling_classic and l2cap_create_signaling_le