reported by Matthias Scheler <tron@lyssa.owl.de> in PR kern/6772.
- After receiving, check whether the receive DMA pointer became 0
what obviously happens if the list runs out of entries. Simply reinit
in this case. This fixes receive lockups after DDB use observed
by myself.
Unstall the receive engine if the ELINK_UPPKTSTATUS indicates that it
was stalled. (Don't know when this might happen. FreeBSD does so.)
9b1eddc4f1