Please apply attached patch.

Without patch, bogus descriptors are parsed as soon as
tp->cur_tx%NUM_TX_DESC + (tp->cur_tx - tp->dirty_tx) > NUM_TX_DESC
(assume for instance tp->dirty_tx = NUM_TX_DESC/2,
tp->cur_tx = NUM_TX_DESC - 1 and watch entry go beyond NUM_TX_DESC).

Missing stats update is fixed by the patch btw.