samples/bpf: Add quiet option to xdpsock

Add a quiet option (-Q) that disables the statistics print outs of
xdpsock. This is good to have when measuring 0% loss rate performance
as it will be quite terrible if the application uses printfs.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/1599726666-8431-4-git-send-email-magnus.karlsson@gmail.com