[Bug] heap-overflow in get.c:344

[chluo1997]

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Describe the bug
A clear and concise description of what the bug is.
There is a heap-overflow bug in get_ipv6_next. Different from #716 (The crash point is in line 322, ntohs(eth_hdr->ether_type);), this bug is triggered in line 344 (pktdata[l2_net_off] >> 4).

To Reproduce
Steps to reproduce the behavior:

1. export CC=clang && export CFLAGS="-fsanitize=address -g"
2. ./autogen.sh && ./configure --disable-shared --disable-local-libopts && make clean && make -j8
3. tcpprep --auto=bridge --pcap=POC --cachefile=/dev/null

Expected behavior
A clear and concise description of what you expected to happen.
The program does not crash.

Screenshots
If applicable, add screenshots to help explain your problem.

System (please complete the following information):

• OS: Debian
• OS version: buster
• Tcpreplay Version: 09f0774

Additional context
Add any other context about the problem here.
POC
poc.zip

[fklassen]

Fixed overflow in PR #744