Add support for static routing.
Documentation in src/networks/model-net/doc/README.fattree.txt This commit is joint work by Jens Domke and Nikhil Jain. Jens did all the ground work for dumping the topology and reading the routing tables. He also wrote the scripts that perform the intermediate steps that generate the routing tables using the topology. Nikhil integrated Jens's changes into CODES by breaking them into a 3 step process as described in src/networks/model-net/doc/README.fattree.txt. Change-Id: I1478fb2ab83b9ded0673d8f897e09a423868795a