netlink: Cache native endianness during init

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
netlink: Extract message checks into reusable method

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
netlink: Cleanup veth pair created during tests

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Merge pull request #190 from titanous/netlink-cleanup

Netlink cleanup