Bluetooth: host: Deprecate BT_LE_ADV defines in hci.h in favour of gap.h

Deprecate BT_LE_ADV defines in hci.h that are expected to be used by the
application in the scan received callback to identify the advertising
PDU type. These defines are mixing HCI input parameters and advertising
PDU types. Internally it is acceptable to mix these, but at the API we
should to mix in them.

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