Switch to scapy with python 3.

Use consistent address schema with local and remote machine. Fill
variables with example IPs from my daily test run.

Use a simpler expression to check the ether type in scapy. This
makes the fragment tests work on FreeBSD. From Ilya Bakulin.

Add test suite for IPv6 neighbor discovery protocol. Send all kind
of solicitations to remote host and check responses. This can be
used to test both pf neighbor discovery states and the IPv6 stack.