WR-NIC was almost out of Block RAM when sythesis was done with chipscope. Then
ISE was trying to pack descriptors' buffers in wrsw_nic into distributed RAM
instead of block RAM. As a result FSMs inside wrsw_nic were able to read
descriptors written by the linux driver, but linux driver was not able to read
updated descriptors written by FSMs. This commit fixes this problem by reducing
the amount of RAM utilized by chipscope cores.