net: have ipconfig not wait if no dev is available

previous commit 3fb72f1e
makes IP-Config wait for carrier on at least one network device.

Before waiting (predefined value 120s), check that at least one device
was successfully brought up. Otherwise (e.g. buggy bootloader
which does not set the MAC address) there is no point in waiting
for carrier.

Cc: Micha Nelissen <micha@neli.hopto.org>
Cc: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Gerlando Falauto <gerlando.falauto@keymile.com>
Signed-off-by: David S. Miller <davem@davemloft.net>