Enable clang-tidy for libsysutils.

Enable the same warnings used elsewhere in the tree, and fix the
two warnings it found (two safe uses of strcpy and one use of
atoi).

Test: builds, boots
Test: atest libsysutils_tests
Test: atest --test-mapping system/netd
Change-Id: I8e5d04da20cc4127439ad9fbda0e4e64f0e671d3