be2net: cleanup and refactor stats code

In preparation for 64-bit stats interface, the following cleanups help
streamline the code:
1) made some more rx/tx stats stored by driver 64 bit
2) made some HW stas (err/drop counters) stored in be_drv_stats 32 bit to
   keep the code simple as BE provides 32-bit counters only.
3) removed duplication of netdev stats in ethtool
4) removed some un-necessary stats and fixed some names

Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>