The "LEN" field is the "length of the MAC frame", in bytes; confusingly,
it includes the extended header length, but not the fixed-length part of
the header (including the FCS), so it's not the "length after HCS".
Rename it to "docsis.len", as it's always LEN, not SID; there's a
separate field for the SID.
Rename the Extended Header Length field to docsis.ehdrlen, and the
Number of Concatenated Frames to docsis.concat_cnt, so that different
uses of the "MACPARM" part of the header are flagged differently.
Update some comments while we're at it.
Change-Id: Ib7c4a0cda65cef25dcaf0051b3de89758ef4c29c
Reviewed-on: https://code.wireshark.org/review/9881
Reviewed-by: Guy Harris <guy@alum.mit.edu>
504f5b3478