lightweight scan strategy - libnet?

I've got an embedded system on which I want to host a very lightweight
and fast SMB scanner.  This scanner will need to ping a large number
(hundreds, potentially thousands) of IP addresses, and for each host
that replies it will try connecting to port 139, just to see if it is
open.  That's all this program has to do.

If I want to maximize speed and simplicity, do you think that libnet
is the right way to inject packets?  It doesn't appear that libnet has
a facility for getting replies --- is there a more suitable library
that does?

Thanks,
Dave