lib/ovs/bridge: Return multiple controllers
lib/ovs/bridge: Return multiple controllers

OVSBridge may have more than one controller. Let get_controller()
return a list of controllers in such cases.

NOTE: this introduces incompatibility if multiple controllers are
configured for a bridge.

Signed-off-by: IWAMOTO Toshihiro <8e41ae29694291a01b8efca6b4a0005a87ddb93e@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

lagopus/ryu-lagopus-ext,lagopus/ryu-lagopus-ext,lagopus/ryu-lagopus-ext,fujita/ryu,osrg/ryu,osrg/ryu,osrg/ryu,fujita/ryu,iwaseyusuke/ryu,iwaseyusuke/ryu,osrg/ryu,lagopus/ryu-lagopus-ext,fujita/ryu,lagopus/ryu-lagopus-ext,iwaseyusuke/ryu,fujita/ryu,iwaseyusuke/ryu,iwaseyusuke/ryu,fujita/ryu,osrg/ryu