bgp: simplify CLUSTER_LIST attribute parser
bgp: simplify CLUSTER_LIST attribute parser

Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

umkcdcrg01/ryu_openflow,gareging/SDN_Framework,alanquillin/ryu,alanquillin/ryu,diogommartins/ryu,castroflavio/ryu,lsqtongxin/ryu,osrg/ryu,takahashiminoru/ryu,Tejas-Subramanya/RYU_MEC,gareging/SDN_Framework,Tejas-Subramanya/RYU_MEC,zangree/ryu,castroflavio/ryu,yamt/ryu,evanscottgray/ryu,takahashiminoru/ryu,fkakuma/ryu,diogommartins/ryu,jazzmes/ryu,haniehrajabi/ryu,sivaramakrishnansr/ryu,iwaseyusuke/ryu,jkoelker/ryu,habibiefaried/ryu,fkakuma/ryu,haniehrajabi/ryu,ttsubo/ryu,umkcdcrg01/ryu_openflow,lzppp/mylearning,alyosha1879/ryu,iwaseyusuke/ryu,evanscottgray/ryu,ttsubo/ryu,shinpeimuraoka/ryu,ttsubo/ryu,openvapour/ryu,StephenKing/ryu,jazzmes/ryu,darjus-amzn/ryu,openvapour/ryu,elahejalalpour/ELRyu,Tesi-Luca-Davide/ryu,muzixing/ryu,openvapour/ryu,hisaharu/ryu,TakeshiTseng/ryu,alyosha1879/ryu,ysywh/ryu,pichuang/ryu,gopchandani/ryu,gareging/SDN_Framework,takahashiminoru/ryu,lagopus/ryu-lagopus-ext,evanscottgray/ryu,StephenKing/summerschool-2015-ryu,Zouyiran/ryu,OpenState-SDN/ryu,John-Lin/ryu,muzixing/ryu,sivaramakrishnansr/ryu,ynkjm/ryu,iwaseyusuke/ryu,Zouyiran/ryu,Tesi-Luca-Davide/ryu,zyq001/ryu,jkoelker/ryu,takahashiminoru/ryu,fujita/ryu,yamt/ryu,openvapour/ryu,gopchandani/ryu,Tejas-Subramanya/RYU_MEC,jalilm/ryu,hisaharu/ryu,lzppp/mylearning,Tejas-Subramanya/RYU_MEC,John-Lin/ryu,fkakuma/ryu,jalilm/ryu,elahejalalpour/ELRyu,lsqtongxin/ryu,jazzmes/ryu,Tejas-Subramanya/RYU_MEC,gopchandani/ryu,habibiefaried/ryu,pichuang/ryu,gopchandani/ryu,osrg/ryu,StephenKing/summerschool-2015-ryu,StephenKing/summerschool-2015-ryu,elahejalalpour/ELRyu,iwaseyusuke/ryu,sivaramakrishnansr/ryu,muzixing/ryu,StephenKing/summerschool-2015-ryu,zyq001/ryu,John-Lin/ryu,habibiefaried/ryu,habibiefaried/ryu,fujita/ryu,alyosha1879/ryu,lzppp/mylearning,ynkjm/ryu,gopchandani/ryu,TakeshiTseng/ryu,haniehrajabi/ryu,lsqtongxin/ryu,yamt/ryu,Tesi-Luca-Davide/ryu,umkcdcrg01/ryu_openflow,zyq001/ryu,ttsubo/ryu,umkcdcrg01/ryu_openflow,ysywh/ryu,zangree/ryu,shinpeimuraoka/ryu,ynkjm/ryu,zyq001/ryu,Zouyiran/ryu,fujita/ryu,castroflavio/ryu,John-Lin/ryu,zangree/ryu,openvapour/ryu,pichuang/ryu,umkcdcrg01/ryu_openflow,darjus-amzn/ryu,yamt/ryu,Tesi-Luca-Davide/ryu,alyosha1879/ryu,sivaramakrishnansr/ryu,elahejalalpour/ELRyu,pichuang/ryu,jalilm/ryu,pichuang/ryu,StephenKing/ryu,lsqtongxin/ryu,OpenState-SDN/ryu,alanquillin/ryu,sivaramakrishnansr/ryu,lagopus/ryu-lagopus-ext,muzixing/ryu,zangree/ryu,ysywh/ryu,fujita/ryu,habibiefaried/ryu,jalilm/ryu,diogommartins/ryu,Zouyiran/ryu,elahejalalpour/ELRyu,lagopus/ryu-lagopus-ext,osrg/ryu,ynkjm/ryu,zangree/ryu,StephenKing/ryu,muzixing/ryu,takahashiminoru/ryu,ttsubo/ryu,ysywh/ryu,StephenKing/summerschool-2015-ryu,lzppp/mylearning,ynkjm/ryu,diogommartins/ryu,gareging/SDN_Framework,darjus-amzn/ryu,gareging/SDN_Framework,haniehrajabi/ryu,darjus-amzn/ryu,lzppp/mylearning,alanquillin/ryu,Zouyiran/ryu,hisaharu/ryu,fujita/ryu,haniehrajabi/ryu,jalilm/ryu,zyq001/ryu,fkakuma/ryu,fkakuma/ryu,lsqtongxin/ryu,shinpeimuraoka/ryu,OpenState-SDN/ryu,lagopus/ryu-lagopus-ext,darjus-amzn/ryu,iwaseyusuke/ryu,hisaharu/ryu,hisaharu/ryu,alanquillin/ryu,TakeshiTseng/ryu,John-Lin/ryu,osrg/ryu,shinpeimuraoka/ryu,TakeshiTseng/ryu,diogommartins/ryu,yamt/ryu,ysywh/ryu,OpenState-SDN/ryu,Tesi-Luca-Davide/ryu,osrg/ryu,TakeshiTseng/ryu,lagopus/ryu-lagopus-ext,jkoelker/ryu,shinpeimuraoka/ryu,OpenState-SDN/ryu,StephenKing/ryu,StephenKing/ryu