Look at subnets, not interfaces, for gateway

Look at the subnet settings to determine the IPs we have on each
network, instead of looking at the interface settings which might not
yet be populated fully.

Change-Id: I2318c3037cd9a2cd959bd238835a0d605560c110
remove obsolete code

Change-Id: I9c094e84cbe9b83f31c5863bda0af8721d09e2ea
Merge pull request #148 from dhellmann/handle-missing-addresses

Look at subnets, not interfaces, for gateway