CVE-2017-13049/Rx: add a missing bounds check for Ubik

[tcpdump] / tests / zephyr-oobr.out

00:16:ca:92:12:01 > 00:15:e8:97:b2:01, ethertype IPv4 (0x0800), length 65535: (tos 0x0, ttl 124, id 16059, offset 0, flags [none], proto UDP (17), length 65521)
    167.155.6.190.2104 > 167.155.9.153.514: [udp sum ok]