ixgbe: remove marketing names from busy poll code

This patch renames the LL_EXTENDED_STATS and some of the functions required to
implement busy polling in the ixgbe driver, in order to remove the marketing
"low latency" blurb which hides what the code actually does.

This furthers work which was requested by Linus Torvalds when the initial busy
poll code was included in the kernel. The code in the ixgbe driver itself was
never properly renamed to reflect the change to busy polling as the title.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>