sunvnet: only use connected ports when sending

The sunvnet driver doesn't check whether or not a port is connected when
transmitting packets, which results in failures if a port fails to connect
(e.g., due to a version mismatch). The original code also assumes
unnecessarily that the first port is up and a switch, even though there is
a flag for switch ports.

This patch only matches a port if it is connected, and otherwise uses the
switch_port flag to send the packet to a switch port that is up.

Signed-off-by: David L Stevens <david.stevens@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>