em revision 7.0.0:
	- Using driver devclass, seperate legacy (pre-pcie) code
	  into a seperate source file. This will at least help
	  protect against regression issues. It compiles along
	  with em, and is transparent to end use, devices in each
	  appear to be 'emX'. When using em in a modular form this
	  also allows the legacy stuff to be defined out.
	- Add tx and rx rings as in igb, in the 82574 this becomes
	  actual multiqueue for the first time (2 queues) while in
	  other PCIE adapters its just make code cleaner.
	- Add RX mbuf handling logic that matches igb, this will
	  eliminate packet drops due to temporary mbuf shortage.

igb revision 1.9.3:
	- Following the ixgbe code, use a new approach in what
	  was called 'get_buf', the routine now has been made
	  independent of rxeof, it now does the update to the
	  engine TDT register, this design allows temporary
	  mbuf resources to become non-critical, not requiring
	  a packet to be discarded, instead it just returns and
	  does not increment the tail pointer.
	- With the above change it was also unnecessary to keep
	  'spare' maps around, since we do not have the discard
	  issue.
	- Performance tweaks and improvements to the code also.

MFC in a week