Bluetooth: report the right security level in getsockopt

During a security level elevation we need to keep track of the current
security level of a connection until the new one is not confirmed.

Signed-off-by: Gustavo Padovan <gustavo@padovan.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>