MFC if_hme.c:1.44, if_hmereg.h:1.7, if_hmevar.h:1.9 to RELENG_6:

• Convert hme(4) to use TX side bus_dmamap_load_mbuf_sg(9).
• Move hardware counter reading/zeroing to hme_tick(). This saves 8 register access per interrupt. [1]
• Use imax macro for getting max. argument between two integers.
• Invoke bus_dmamap_sync(9) first before freeing mbuf.
• Check driver queue first to reduce locking operation in hme_start_locked() and interrupt handler.
• Simplyfy watchdog timer setup in interrupt handler.
• Don't log normal errors such as RX overrun. If we have DMA stuck condition, reinitialize the driver and log it.