User networking: Show active connections

In case you're wondering what connections exactly you have open
or maybe redir'ed in the past, you can't really find out from qemu
right now.

This patch enables you to see all current connections the host
only networking holds open, so you can kill them using the previous
patch.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>