allow recovery from transmission lockups which occur in the middle
of the descriptor list, rather than just at the beginning.
For some unknown reason, Rhine II chips have a tendency to stop
transmitting while under heavy load, possibly due to collisions.
Whether this behavior is due to a hardware bug or a driver glitch
is unknown as of now.
In either case, this change allows the driver to gracefully recover
from such situations.
Special thanks go to The Anarcat <anarcat@anarcat.dyndns.org>, who
bugged me into looking at this and to
Dominic Marks <dominic_marks@btinternet.com>, who performed a great
deal of testing to help characterize this problem.
MFC after: 3 days
000c679b3c