In commit 60c07d93 ("net: fix
qemu_can_send_packet logic") the "VLAN" broadcast behavior was changed
to queue packets if any net client cannot receive.  It turns out that
this was not actually the right fix and just hides the real bug that
hw/usb/dev-network.c:usbnet_receive() clobbers its receive buffer when
called multiple times in a row.  The commit also introduced a new bug
that "VLAN" packets would not be sent if one of multiple net clients was
down.

The hw/usb/dev-network.c bug has since been fixed, so this patch reverts
broadcast behavior to send packets as long as one net client can
receive.  Packets simply get queued for the net clients that are
temporarily unable to receive.
Reported-by: NRoy.Li <rongqing.li@windriver.com>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>