libbpf-tools: fix misuse of bpf_get_current_pid_tgid

libbpf-tools: fix misuse of bpf_get_current_pid_tgid

bpf_get_current_pid_tgid() returns process ID in the upper 32bits,
and thread ID in lower 32 bits (both from userspace's perspective).
biosnoop and gethostlatency misuse this function.
biosnoop takes the thread ID as process ID which is not expected.
gethostlatency uses the process ID as a unique key for BPF map,
which may result in event loss or data corruption.
This commit fixes these problems.

Signed-off-by: Hengqi Chen <chenhengqi@outlook.com>