watchpoint: support kernel watchpoint in absolute address
watchpoint: support kernel watchpoint in absolute address

If there is no related pid, we consider it as a watchpoint
for address in kernel space and attach the bpf program
to perf event on each online CPUs.

Signed-off-by: htbegin <d1e3cfa1a6327d9c98cdfd1b5b28eac8a7187502@gmail.com>

iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace