Extend the syntax of hostfwd_add/remove to optionally take a tuple of
VLAN ID and slirp stack name. If those are omitted, the commands will
continue to work on the first registered slirp stack.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>