packet/gre: Support NVGRE extension
packet/gre: Support NVGRE extension

Signed-off-by: Shinpei Muraoka <154d36ff5308ea67e46435bebcfb51dcc823bd4d@gmail.com>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

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