To enable the use of uncached DMA buffers as RX and TX communication
buffers in between driver (service) and client, introduce a cache
attribute in the constructor of Nic::Session_component
Ref #3291
Some application code is dereferencing the pointer returned by
'packet_content' at packet streams without checking that it is valid.
Throw an exception rather than return a null pointer, except for
zero-length packets, which have somewhat implicit invalid content and
that we believe to be properly handled in all current cases.
The client-side of a packet stream cannot take corrective action if the
server-side is sending packets with invalid content, but the servers
that provide packet streams should catch this exception to detect
misbehaving clients.
Ref #3059
