tools: bpftool: print nb of cmds to stdout (not stderr) for batch mode

tools: bpftool: print nb of cmds to stdout (not stderr) for batch mode

When batch mode is used and all commands succeeds, bpftool prints the
number of commands processed to stderr. There is no particular reason to
use stderr for this, we could as well use stdout. It would avoid getting
unnecessary output on stderr if the standard ouptut is redirected, for
example.

Reported-by: David Beckett <david.beckett@netronome.com>
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>