PduType
PDU type identifies the type of the message.
Bearers may use this type to set the proper value in the payload. For ADV bearer it will be a proper AD Type (see Assigned Numbers / Generic Access Profile), for GATT bearer the correct Message type in the Proxy PDU.
Some message types are handled only by some bearers, for example the provisioning PDU type must be sent using a provisioning bearer(PB type of bearer).