network: Set the link down before its configuration
network: Set the link down before its configuration

This patch makes sure we check if the link found is up or down. In
case it is up, we want to set it down to be able to properly set all
all other parameters provided.

Fixes #36

Signed-off-by: Sebastien Boeuf <90b401417360b1924ef3f520ddee932686110f85@intel.com>

clearcontainers/agent,clearcontainers/agent