Drivers should not modify STREAMS messages
that have been dup'ed.
Such messages can be identified by a reference count
(mp->b_datap->dp_ref)
that is greater than 1.
In MDI-based Ethernet drivers,
frames that are smaller than the minimum length
specified by Ethernet/802.3 must be padded.
Padding should be done by appending bytes
onto the end of a hardware buffer
rather than at the end of a STREAMS message.
To determine the maximum STREAMS message size,
use the STRMSGSIZE flag to the
drv_getparm(D3)
function.