fix(ebpf): start profiling after attaching perf reader

[korniltsev]

There was a tiny time window when we already attach ebpf program to perf event (start profiling) and not yet attached a reader for pid info requests.

So this line some times return 2 (ENOENT) instead of 0, causing userspace program miss some processes to profile.

pyroscope/ebpf/bpf/profile.bpf.c

Line 50 in 8dc366a

bpf_perf_event_output(ctx, &events, BPF_F_CURRENT_CPU, &event, sizeof(event));

This PR changes order of enabling profiling - start reading events first, then start profiling

[kolesnikovae]

LGTM