selftests/bpf: Add test based on port range for BPF flow dissector

Add a simple test to make sure that a filter based on specified port
range classifies packets correctly.

Signed-off-by: Yoshiki Komachi <komachi.yoshiki@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Petar Penkov <ppenkov@google.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200117070533.402240-3-komachi.yoshiki@gmail.com