Enable clang-tidy for clatd.

Enable the same warnings used elsewhere in the tree, and fix two
warnings it found (a safe use of strcpy, and a missing O_CLOEXEC
when opening the tun device node.

Test: builds, boots, clatd works
Test: m clatd clatd_test clatd_microbenchmark && atest clatd_test
Change-Id: I9a5ea4de5f31d3c495871250a6493b07535a604b
5 files changed