net: Print output of "-net nic, model=help" to stdout instead of stderr

net: Print output of "-net nic, model=help" to stdout instead of stderr

We are printing all other help output to stdout already (e.g. "-help",
"-cpu help" and "-machine help" output). So the "-net nic,model=help"
output should go to stdout instead of stderr, too. And while we're at
it, also print the NICs line by line, like we do it e.g. with the
"-cpu help" or "-M help" output, too.

Buglink: https://bugs.launchpad.net/qemu/+bug/1574327
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190423160608.7519-1-thuth@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>