This means no conversion is necessary between the transport_type and
the networkProtocol field of the PortAddress struct. Not currently an
issue, but will be needed for implementing the CLOCK_DESCRIPTION
management TLV.
Although the UDP/IPv4 layer does not need any state per instance (other
than the two file descriptors), the raw Ethernet layer will need this.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>