Bluetooth: pairing: OOB: Separate LE SC OOB from legacy OOB logic

Some systems can support only legacy OOB pairing while others only
LE SC OOB pairing.

The existent API function "bt_set_oob_data_flag" was removed.

Two new API functions were added:

 * "bt_le_oob_set_legacy_flag" to signal that legacy OOB pairing is used
 * "bt_le_oob_set_sc_flag" to signal that LE SC OOB pairing is used

The code will now advertise the presence of OOB flag depending
on the type of pairing method(SC vs legacy)

Signed-off-by: Sebastian Panceac <sebastian.panceac@ext.grandcentrix.net>