Fix pep8 style issues

Signed-off-by: Joe Stringer <joestringernz@gmail.com>
Remove redundant code

Signed-off-by: Joe Stringer <joe@wand.net.nz>
Use ryu library for parsing packet ethertype

Signed-off-by: Joe Stringer <joe@wand.net.nz>
Use new Ryu topology module to track datapaths

Co-authored-by: raphaelvrosa <raphaelvrosa@gmail.com>
Signed-off-by: Joe Stringer <joe@wand.net.nz>
Choose OpenFlow version based on import

Signed-off-by: Joe Stringer <joe@wand.net.nz>