ivs: add uplink command line option

For non-OpenFlow functionality like in-band management, we need to know which
ports are connected up to the network versus down to a VM.
OVSDriver: mark ports as being uplinks

Also adds interfaces for the forwarding pipeline to check whether a given port
is an uplink and to get the first live uplink.
OVSDriver: bring local interface up after creation
OVSDriver: enable IPv6 on the internal interface
OVSDriver: enable upcalls after other initialization finishes

This prevents us from trying to handle upcalls before the pipeline is
initialized.
ivs: change default datapath name to ivs
Merge into master from pull request #197:
Uplink configuration (https://github.com/floodlight/ivs/pull/197)