- Wrap the handler and associated code for collecting completed RX

- Wrap the handler and associated code for collecting completed RX
  descriptors that are still marked owned in #ifdef GEM_RINT_TIMEOUT
  instead of #if 0 for convenience.
- Remove stale code and comment about relying on the preset XIF config.
- In case of a watchdog timeout call the init function instead of just
  the start function so the chip is properly reset.

Merge from hme(4):
- Convert to use bus_dmamap_load_mbuf_sg() for loading RX buffers.
- Protect from a duplicate mbuf free panic in case the DMA engine hangs.

Reviewed by:	yongari
Tested on:	powerpc(grehan), sparc64
MFC after:	1 week