Added wrappers for following pcap apis.

 - pcap_create
 - pcap_activate
 - pcap_set_buffer_size
 - pcap_set_promisc
 - pcap_timeout
 - pcap_set_snaplen
Modified pcap capture unit test log msgs.
gofmt pcap.go, pcap_test.go.
Merge pull request #5 from anoopk6/master

Pcap api additions