CVE-2017-13687/CHDLC: Improve bounds and length checks.

[tcpdump] / tests / rpl-19-pickdagvvv.out

IP6 (hlim 64, next-header ICMPv6 (58) payload length: 56) fe80::216:3eff:fe11:3424 > fe80::216:3eff:fe11:3424: [icmp6 sum ok] ICMP6, RPL, (CLR)Destination Advertisement Object [dagid:5431::,seq:10,instance:42,Dagid,40] opt:rpltarget len:25  0x0000:  0080 2001 0db8 0001 0000 0216 3eff fe11 0x0010:  3424 0000 0000 00 opt:pad0 opt:pad0 opt:pad0 opt:pad0 opt:pad0 opt:pad0 opt:pad0