/usr/src/linux-headers-4.4.0-63-lowlatency/kernel/irq is in linux-headers-4.4.0-63-lowlatency 4.4.0-63.84.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-headers-4.4.0-63-lowlatency/kernel/../../linux-headers-4.4.0-63/kernel/irq