added string helpers for link key and link key type from Christian Wick

git-svn-id: http://btstack.googlecode.com/svn/trunk@2862 1a0a8af8-31b5-11de-8e0c-53a27eea117e
fix format for GATT_ALL_CHARACTERISTIC_DESCRIPTORS_QUERY_RESULT

git-svn-id: http://btstack.googlecode.com/svn/trunk@2863 1a0a8af8-31b5-11de-8e0c-53a27eea117e