controller: fix that sender thread is never terminated
controller: fix that sender thread is never terminated

Empty q.get() is blocking send thread.
Because of this issue, datapath state never transit to DEAD.

This fixes commit 83e3709a0d70f889e794d1c5f70c1c1eb73075f7.
  - controller: fix send_q draining
      https://github.com/osrg/ryu/commit/83e3709a0d70f889e794d1c5f70c1c1eb73075f7

Signed-off-by: YAMADA Hideki <382f20a79c68ed60a19800d5b0d5057a221748a0@po.ntts.co.jp>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

jkoelker/ryu,takahashiminoru/ryu,evanscottgray/ryu,StephenKing/summerschool-2015-ryu,ynkjm/ryu,iwaseyusuke/ryu,citrix-openstack-build/ryu,openvapour/ryu,lzppp/mylearning,ysywh/ryu,osrg/ryu,gareging/SDN_Framework,ntts-clo/ryu,fujita/ryu,diogommartins/ryu,habibiefaried/ryu,StephenKing/summerschool-2015-ryu,ynkjm/ryu,shinpeimuraoka/ryu,gareging/SDN_Framework,John-Lin/ryu,takahashiminoru/ryu,pichuang/ryu,darjus-amzn/ryu,diogommartins/ryu,fkakuma/ryu,lsqtongxin/ryu,pichuang/ryu,haniehrajabi/ryu,ysywh/ryu,habibiefaried/ryu,lzppp/mylearning,gopchandani/ryu,iwaseyusuke/ryu,zangree/ryu,Zouyiran/ryu,OpenState-SDN/ryu,pichuang/ryu,fkakuma/ryu,unifycore/ryu,takahashiminoru/ryu,sivaramakrishnansr/ryu,habibiefaried/ryu,Zouyiran/ryu,elahejalalpour/ELRyu,haniehrajabi/ryu,haniehrajabi/ryu,ynkjm/ryu,TakeshiTseng/ryu,zyq001/ryu,alanquillin/ryu,lagopus/ryu-lagopus-ext,sivaramakrishnansr/ryu,StephenKing/ryu,jalilm/ryu,StephenKing/summerschool-2015-ryu,ynkjm/ryu,zyq001/ryu,yamada-h/ryu,mikhaelharswanto/ryu,zangree/ryu,StephenKing/ryu,Tejas-Subramanya/RYU_MEC,sivaramakrishnansr/ryu,takahashiminoru/ryu,darjus-amzn/ryu,Tejas-Subramanya/RYU_MEC,jazzmes/ryu,mikhaelharswanto/ryu,sivaramakrishnansr/ryu,ttsubo/ryu,osrg/ryu,ttsubo/ryu,John-Lin/ryu,citrix-openstack/build-ryu,elahejalalpour/ELRyu,John-Lin/ryu,shinpeimuraoka/ryu,alyosha1879/ryu,gareging/SDN_Framework,habibiefaried/ryu,ykaneko/ryu,umkcdcrg01/ryu_openflow,castroflavio/ryu,citrix-openstack/build-ryu,evanscottgray/ryu,fujita/ryu,yamt/ryu,Zouyiran/ryu,openvapour/ryu,hisaharu/ryu,muzixing/ryu,umkcdcrg01/ryu_openflow,castroflavio/ryu,Tesi-Luca-Davide/ryu,muzixing/ryu,Tejas-Subramanya/RYU_MEC,ysywh/ryu,gareging/SDN_Framework,lzppp/mylearning,iwaseyusuke/ryu,OpenState-SDN/ryu,samrussell/ryu,gopchandani/ryu,ynkjm/ryu,alanquillin/ryu,ntts-clo/mld-ryu,yamada-h/ryu,muzixing/ryu,zangree/ryu,elahejalalpour/ELRyu,hisaharu/ryu,alyosha1879/ryu,diogommartins/ryu,elahejalalpour/ELRyu,gopchandani/ryu,osrg/ryu,alanquillin/ryu,ntts-clo/mld-ryu,lsqtongxin/ryu,shinpeimuraoka/ryu,jalilm/ryu,elahejalalpour/ELRyu,jalilm/ryu,gareging/SDN_Framework,hisaharu/ryu,haniehrajabi/ryu,zangree/ryu,iwaseyusuke/ryu,lagopus/ryu-lagopus-ext,yamt/ryu,jalilm/ryu,zyq001/ryu,citrix-openstack-build/ryu,fujita/ryu,gopchandani/ryu,habibiefaried/ryu,fujita/ryu,ysywh/ryu,lsqtongxin/ryu,lzppp/mylearning,ntts-clo/ryu,fkakuma/ryu,torufuru/OFPatchPanel,OpenState-SDN/ryu,ttsubo/ryu,jazzmes/ryu,lsqtongxin/ryu,takahashiminoru/ryu,alanquillin/ryu,fkakuma/ryu,torufuru/OFPatchPanel,fujita/ryu,torufuru/oolhackathon,muzixing/ryu,ttsubo/ryu,fkakuma/ryu,StephenKing/ryu,o3project/ryu-oe,umkcdcrg01/ryu_openflow,osrg/ryu,diogommartins/ryu,alyosha1879/ryu,StephenKing/summerschool-2015-ryu,Zouyiran/ryu,StephenKing/ryu,castroflavio/ryu,iwaseyusuke/ryu,haniehrajabi/ryu,jkoelker/ryu,zangree/ryu,darjus-amzn/ryu,darjus-amzn/ryu,lzppp/mylearning,openvapour/ryu,openvapour/ryu,Zouyiran/ryu,shinpeimuraoka/ryu,sivaramakrishnansr/ryu,StephenKing/summerschool-2015-ryu,TakeshiTseng/ryu,Tesi-Luca-Davide/ryu,ysywh/ryu,hisaharu/ryu,unifycore/ryu,John-Lin/ryu,darjus-amzn/ryu,muzixing/ryu,umkcdcrg01/ryu_openflow,pichuang/ryu,openvapour/ryu,gopchandani/ryu,yamt/ryu,lagopus/ryu-lagopus-ext,ykaneko/ryu,diogommartins/ryu,evanscottgray/ryu,jalilm/ryu,Tesi-Luca-Davide/ryu,lsqtongxin/ryu,OpenState-SDN/ryu,torufuru/oolhackathon,TakeshiTseng/ryu,Tesi-Luca-Davide/ryu,StephenKing/ryu,OpenState-SDN/ryu,Tesi-Luca-Davide/ryu,Tejas-Subramanya/RYU_MEC,samrussell/ryu,lagopus/ryu-lagopus-ext,torufuru/oolhackathon,TakeshiTseng/ryu,yamt/ryu,John-Lin/ryu,TakeshiTseng/ryu,Tejas-Subramanya/RYU_MEC,zyq001/ryu,ttsubo/ryu,yamt/ryu,hisaharu/ryu,o3project/ryu-oe,shinpeimuraoka/ryu,alyosha1879/ryu,jazzmes/ryu,lagopus/ryu-lagopus-ext,pichuang/ryu,jkoelker/ryu,zyq001/ryu,umkcdcrg01/ryu_openflow,osrg/ryu,alanquillin/ryu