Bluetooth: Move IRK checking logic in preparation to new connect method

Move IRK checking logic in preparation to new connect method. Also
make sure that MGMT_STATUS_INVALID_PARAMS is returned when non
identity address is passed to ADD_DEVICE. Right now MGMT_STATUS_FAILED
is returned, which might be misleading.

Signed-off-by: Jakub Pawlowski <jpawlowski@google.com>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>