Add a few MAC checks

Notably mac.is_multicast() which is needed for TAPs / LCPs and
interfaces.

Add a test for interface MAC addresses being non-multicast.

README.md

@@ -17,6 +17,8 @@ sudo pip3 install argparse
 sudo pip3 install yamale
 sudo pip3 install pyyaml
 sudo pip3 install pyinstaller
+sudo pip3 install netaddr
+sudo pip3 install ipaddress
 
 ## Ensure all unittests pass.
 ./tests.py -d -t unittest/yaml/*.yaml