Enable access to 169.254.169.254 directly over the physcial interface

Some Linux system images assume that 169.254.0.0/16 is reachable directly
over the physcial interface (this is the default behavior in nova-network).
This patch bring backs this behavior to quantum based network.
Merge pull request #72 from tpaszkowski/pull-req-dhcp-agent-enable-metatdata-network

Enable access to 169.254.169.254 directly over the physcial interface