Bluetooth: Host: Fix GATT server handling of CCC

GATT server was not doing enough check before udpating the CCC.

For example, a non-bonded client could update the CCC of a bonded client
by spoofing his address.

This fix the issue by dissociating the CCC configuration of a bonded and
a non-bonded peer. To do that, a new field is added to the CCC config:
`link_encrypted`.

Signed-off-by: Théo Battrel <theo.battrel@nordicsemi.no>