bgp: Prevent __str__() methods from raising exceptions
bgp: Prevent __str__() methods from raising exceptions

bgp.BadMsg.__str__(): avoid "AttributeError: 'BadMsg' object has no attribute 'msg'"

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

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