This commit extends the existing DUP11/DPV11 support to add support for HDLC framing. There
is no requirement to support bit/byte stuffing, so the aim is simply to encapsulate/decapsulate
the datalink frame provided by the host driver.
DDCMP has been regression tested on VMS, RSX and TOPS20, and the HDLC mode was developed
and tested with VAX/VMS DECnet Phase V, only using the HDLC datalink implementation.
In theory this support is sufficient to allow Phase IV/V P.S.I and even VMS/SNA to be used,
but these remain to be demonstrated.
16943b4582