The check in qemu_can_send_packet() does not work correctly when using 
multiple nics.  I found the problem when using -boot n and having more 
than one nic in use with the SLIRP networking.  The 
qemu_can_send_packet() is only called as a part of the SLIRP networking 
check to see if there is a valid interface that packets can be sent on.

Using the attached patch, a pxe boot can be used with more than one nic, 
in particular using nics of different types.  I also tested to make sure 
it still worked with a single nic as well.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

Jason.