add more debug messages for user-level rx processing
add wmb and loop count in polling loops
fix a bug that may lead to inconsistency of prod pointer
add safe return with error while axi doens't respond for a while
enable pci reset in up handler to avoid inconsistency with DMA engine

- without it, if ifconfig up and down, all rx buffers are reinitialized
  and pointers are reset, so some inconsistency might happen.
Merge branch 'master' into tx_batching
Merge branch 'tx_batching' of https://github.com/NetFPGA-NewNIC/linux-driver into tx_batching