traffic_layout/engine: add missing stat import
We were using `mode_t` without it being available on some architectures.
tscore/ink_hrtime: add missing cstdint import
On alpine linux 3.9 (and edge) the compilation was failing
because of a missing import.
tscore/eventnotify: change fcntl include path
The default include path for `fnctl.h` changed some time in the 90's.