cxgb3i: Fix a login over vlan issue

Fix a target login issue, when parent interface is vlan and we are using cxgb3i sepecific
private ip address in '/etc/iscsi/ifaces/' iface file.

Acked-by: Karen Xie <kxie@chelsio.com>
Signed-off-by: Rakesh Ranjan <rakesh@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>