hardirqs: fix issue if irq is triggered while idle task (tid=0)

hardirqs: fix issue if irq is triggered while idle task (tid=0)

Currently, hardirqs use tid as key to store information while tracepoint
irq_handler_entry. It works fine if irq is triggered while normal task
running, but there is a chance causing overwrite issue while irq is
triggered while idle task (a.k.a swapper/x, tid=0) running on multi-core
system.

Let's say there are two irq event trigger simultaneously on both CPU
core, irq A @ core #0, irq B @ core #1, and system load is pretty light,
so BPF program will get tid=0 since current task is swapper/x for both cpu
core. In this case, the information of first irq event stored in map could
be overwritten by incoming second irq event.

Use tid and cpu_id together to make sure the key is unique for each
event in this corner case.

Please check more detail at merge request #2804, #3733.