RDMA/nes: Turn carrier off on ifdown

This lets the bonding driver to detect when an interface goes down.

Signed-off-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: Chien Tung <chien.tin.tung@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>