NFE - Change default RX ring size from 128 -> 256, Adjust moderation timer.

NFE - Change default RX ring size from 128 -> 256, Adjust moderation timer.

* NFE does not seem to be able to flow control the phy.  TCP reception
  using window scaling and large socket bufs can blow out the receiver ring
  before the interrupt has a chance to drain it.

  This results in the receiver dropping a packet and the transmitter
  seeing bursts of duplicate TCP acks and having to go into recovery.

* Shorten the moderation timer from 500uS to 250uS, increasing its
  frequency from 2000Hz to 4000Hz.  Note that the moderation timer
  only kicks in when the discrete interrupt rate exceeds the frequency.

* The problem still occurs with the larger RX ring and shorter moderation
  timer, but not nearly as often.