packet/bgp: Fix default of esi for IP Prefix route
packet/bgp: Fix default of esi for IP Prefix route

"esi" value should be an instance of EvpnEsi subclass and not int
type value, this patch fixes the default value to "None".

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

iwaseyusuke/ryu,lagopus/ryu-lagopus-ext,shinpeimuraoka/ryu,osrg/ryu,gareging/SDN_Framework,pichuang/ryu,iwaseyusuke/ryu,osrg/ryu,shinpeimuraoka/ryu,lagopus/ryu-lagopus-ext,shinpeimuraoka/ryu,iwaseyusuke/ryu,fujita/ryu,pichuang/ryu,shinpeimuraoka/ryu,gareging/SDN_Framework,pichuang/ryu,pichuang/ryu,osrg/ryu,osrg/ryu,iwaseyusuke/ryu,fujita/ryu,pichuang/ryu,fujita/ryu,gareging/SDN_Framework,lagopus/ryu-lagopus-ext,fujita/ryu,lagopus/ryu-lagopus-ext,gareging/SDN_Framework,shinpeimuraoka/ryu,fujita/ryu,osrg/ryu,gareging/SDN_Framework,iwaseyusuke/ryu,lagopus/ryu-lagopus-ext