ixgbe: new vectorized functions for Rx/Tx

ixgbe: new vectorized functions for Rx/Tx

New file containing optimized receive and transmit functions which
use 128bit vector instructions to improve performance. When conditions
permit, these functions will be enabled at runtime by the device
initialization routines already in the PMD.

The compilation of the vectorized RX and TX code paths is controlled by
a new setting in the build time configuration for the IXGBE driver. Also
added is a setting which allows an optional further performance increase
by disabling the use of the olflags field on packet RX.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: XiaonanX Zhang <xiaonanx.zhang@intel.com>
Tested-by: Waterman Cao <waterman.cao@intel.com>
[Thomas: code-style adjustments]
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>