packet/icmpv6: Assert length in options are valid
packet/icmpv6: Assert length in options are valid

About the 'length' field in ICMPv6 options,
RFC4861 says that "The value 0 is invalid".
This patch adds assertions to raise a exception
for such invalid ICMPv6 packets.

Reported-by: William Fisher <71ab9f8fc17cf8b5565a40878b4c0d8249d6608d@gmail.com>
Reported-by: Shivaram Mysore <378da60335efa6b71b5c7dce6a8133fe73915c1e@gmail.com>
Signed-off-by: Satoshi Fujimoto <cd75558e8cccb245feb2368a5a53f09e4ecc2257@gmail.com>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

lagopus/ryu-lagopus-ext,fujita/ryu,fujita/ryu,iwaseyusuke/ryu,lagopus/ryu-lagopus-ext,iwaseyusuke/ryu,fujita/ryu,osrg/ryu,osrg/ryu,fujita/ryu,iwaseyusuke/ryu,osrg/ryu,fujita/ryu,iwaseyusuke/ryu,lagopus/ryu-lagopus-ext,lagopus/ryu-lagopus-ext,osrg/ryu,lagopus/ryu-lagopus-ext,osrg/ryu,iwaseyusuke/ryu