Move btstack_linked_queue into core, mention in Changelog

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - GAP: LE Whitelist API with 'gap_le_whitelist_x' with x = add, remove, clear and new `gap_connect_with_whitelist`
 - SDP Client: add sdp_client_register_query_callback() allows to register query request instead of polling sdp_client_ready()
 - BNEP lwIP: add `bnep_lwip_connect` to establish BNEP connection and manage lwIP network interface
+- New `btstack_linked_queue` utility, a linked list-based queue with first-in-first-out semantics and constant time enqueue/dequeue operations
 
 ### Changed
 - GAP: treat AES-CCM encrypted connection as mutually authenticated (BIAS)