The #2418 has changed a behaviour of "weave ps" which outputs
"Link not found" in the case of weave not running. The previous
behaviour was to output an empty line.
- Optimize. Use LinkByName instead of iterating over list of available
links. Linux does not support interfaces with the same names.
- Remove unnecessary indirection in utility functions which return
common.NetDev.
Also move netlink and netns code from common to net
Creates interface if not already there
Adds addresses
Move the set link 'up' to after addresses are added