This allows to configure bluetoothd to require minimum encryption key
size when accessing GATT server characteristics. It is a global
configuration option affecting whole GATT database.
This makes the ready callbacks much more convenient to track when the
client is ready since its is now possible to notify more than on client
at the same time.
Due to the issues with CSRK tests ext_signed flag has been added to
allow android/gatt handle signed write operations.
This patch fixes following tests:
GAP__TC_SEC_CSIGN_BV_02_C
GAP__TC_SEC_CSIGN_BI_01_C
GAP__TC_SEC_CSIGN_BI_02_C
GAP__TC_SEC_CSIGN_BI_03_C
GAP__TC_SEC_CSIGN_BI_04_C
SM__TC_SIGN_BV_03_C