Fix latency measurement for IPv6
Fix latency measurement for IPv6

 * Correct checksum calculations and apply UDP checksum as well.

 * Ensure the minimum packet size must be able to contain latency magic
   number and timestamps.  (This becomes an issue with IPv6 packets.)

 * Add non-zero values to IPv6 source addresses.

 * Update DPDK's rx_conf/tx_conf mode flag names.

ANLAB-KAIST/pspgen-dpdk