wireguard: add burst mode

wireguard: add burst mode

Originally wireguard does packet by packet encryption and decryption.

This patch adds burst mode for encryption and decryption packets. In
addition, it contains some performance improvement such as prefetching
packet header and reducing the number of current time function calls.

Type: improvement

Signed-off-by: Gabriel Oginski <gabrielx.oginski@intel.com>
Change-Id: I04c7daa9b6dc56cd15c789661a64ec642b35aa3f
(cherry picked from commit 8ca08496a43e8d98fe2d4130d760c6fb600d0a93)