Fix tx queue (slist can be corrupted when tx interrupts hit within tx_encap.
Lower interrupt moderation timer to (improves performance).
Improve chip identification. (from linux sk98lin driver).
Keep tx queue running by kicking the tx bmu repeatedly.
From FreeBSD via OpenBSD, port to NetBSD done by Stephen Degler
Changes relative to submitted version:
* yukonreg.h and xmaciireg.h merged into if_skreg.h
* bhack[] constified + other small editing changes
* use 'Ethernet address' rather than 'address' in attach message
XXX completely untested by me, needs further cleanup
Driver provided in PR kern/22511 by Stephen Degler
