Implement pseudo-checksum for IPv4 randomize

before/after:
```
tcpreplay-edit --preload-pcap --intf1=eth7 -t --loop 10 -q -s3   bosTap.pcap
Actual: 7916150 packets (3554177840 bytes) sent in 5.13 seconds.
Rated: 692822208.0 Bps, 5542.58 Mbps, 1543109.12 pps
Statistics for network device: eth7
	Attempted packets:         7916150
	Successful packets:        7916150
	Failed packets:            0
	Truncated packets:         0
	Retried packets (ENOBUFS): 0
	Retried packets (EAGAIN):  0

tcpreplay-edit --preload-pcap --intf1=eth7 -t --loop 10 -q -s3   bosTap.pcap
Actual: 7916150 packets (3554177840 bytes) sent in 4.07 seconds.
Rated: 742194471.9 Bps, 5937.55 Mbps, 1653075.06 pps
Statistics for network device: eth7
	Attempted packets:         7916150
	Successful packets:        7916150
	Failed packets:            0
	Truncated packets:         0
	Retried packets (ENOBUFS): 0
	Retried packets (EAGAIN):  0
```
minor edits - closes #8
Merge pull request #9 from appneta/Enhancement_pseudo_crc

Enhancement pseudo crc