mxge cleanups:

• Remove code to use the special wc_fifo. It has been disabled by default in our other drivers as it actually slows down transmit by a small amount

• Dynamically determine the amount of space required for the rx_done ring rather than hardcoding it.

• Compute the number of tx descriptors we are willing to transmit per frame as the minimum of 128 or 1/4 the tx ring size.

• Fix a typo in the tx dma tag setup which could lead to unnecessary defragging of TSO packets (and potentially even dropping TSO packets due to EFBIG being returned).

• Add a counter to keep track of how many times we've needed to defragment a frame. It should always be zero.

• Export new extended f/w counters via sysctl

Sponsored by: Myricom, Inc.