Bluetooth: host: Log security keys needed by sniffer

Log the security keys that the sniffer needs in order to sucessfully
decrypt the connection.
This option allows the sniffer to work in the cases where enabling
using the SMP debug keys is not wanted, either because it changes the
way the peer behaves or is denied by the peer.
It also enables the sniffer to decrypt a connection where the bond
already exists.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>