First pass rewrite of pcap.go

Lots of idiomatic fixes:
 - remove needless named return parameters
 - reverse annoying `if constantValue == someFunction()`
 - simplify a lot of tortured loop constructs
 - use `defer` across the board for resource cleanup
 - assign struct members at instantiation rather than later
Missed a few fixes in pcap.go
Comment out failing tests (for now)
One obvious vet fix
Missed a fix in pcap.go
go vet and golint fixes
Some renames