LGTM.com alerts about libpcap and tcpdump

[Guy Harris]

(Looks Good To Me? Little Goggle-eyed Tiny Monkey?)

	https://lgtm.com

has a number of open-source projects that it scans, including

	https://lgtm.com/projects/g/the-tcpdump-group/libpcap/?mode=list

(mostly complaints about internal headers lacking header guards) and

	https://lgtm.com/projects/g/the-tcpdump-group/tcpdump/?mode=list

(a lot of complaints about using non-thread-safe time_t interpretation routines; if we care about libnetdissect being thread-safe, that's an issue, and another pile of complaints about headers lacking header guards).