The size of the padded and encapsulated BFD control packets
to be transmitted at Layer 3. The BFD minimum control packet
size is 24 or 26 octets; see Section 6.8.6 of RFC 5880.
If the configured padded PDU size is smaller than the minimum
sized packet of a given BFD session, then the minimum sized
packet for the session will be used.
The maximum padded PDU size may be limited by the supported
interface MTU of the system.