switching from static IP to DHCP on wired config doesn't automatically trigger dhclient

[Chris Hellberg]

Steps to reproduce:

1. set IP address to static on a wired connection
2. IP address is active on the interface
3. set IP address assignment method to DHCP
4. dhclient isn't involved

I would expect this change to happen immediately

root@ubuntu:/var# lsb_release -rd
Description: Ubuntu 12.10
Release: 12.10
root@ubuntu:/var#

root@ubuntu:/var# apt-cache policy network-manager
network-manager:
  Installed: 0.9.6.0-0ubuntu7
  Candidate: 0.9.6.0-0ubuntu7
  Version table:
 *** 0.9.6.0-0ubuntu7 0
        500 http://archive.ubuntu.com/ubuntu/ quantal/main amd64 Packages
        100 /var/lib/dpkg/status
root@ubuntu:/var#