16 RX buffers and 8 TX buffers is probably excessive. Nanostack
version of driver successfully used 4+4, and data pump should be
broadly equivalent.
This means that switching K64F devices from Nanostack to EMAC increases
base heap usage by 18K - observed in Nanostack border router builds.
Add a config option to make it possible to lower the number of buffers.
Defer consideration of lowering the default to later.
Kevin Bracey