33c0d6a luci: Add support for the IP "prefer_interface" attr

Authored and Committed by rmccabe 9 years ago
    luci: Add support for the IP "prefer_interface" attr
    
    Add support for editing the "prefer_interface" attribute of
    the IP resource while in expert mode.
    
    Resolves: rhbz#917738
    
    Signed-off-by: Ryan McCabe <rmccabe@redhat.com>