more unittests
fixed/added unittests for IPv6/IPv4/MAC, fixed getStrings, added +/-/== for ipv4_address
Merge pull request #23 from scholzd/unittests

Unittests + (bugfixes)
add support for checksum offloading

note: udp checksumming doesn't seem to work properly at the moment...
implement udp checksum offloading