RyuBGPSpeaker: Enable to notify BGP events
RyuBGPSpeaker: Enable to notify BGP events

This patch enables RyuBGPSpeaker, which is a base Ryu application for
creating user BGP applications, to notify the BGP events corresponding
to 'best_path_change_handler', 'peer_down_handler' and 'peer_up_handler'
of bgpspeaker.BGPSpeaker.

Signed-off-by: IWASE Yusuke <bb80e84cc9f5a8f01385872ee89032beb5d4eba7@gmail.com>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

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