spice: add config options for the listening address

Make listening address configurable.  Also add options to
force using IPv4 or IPv6.
diff --git a/qemu-config.c b/qemu-config.c
index f52e50c..5a62ae1 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -365,6 +365,15 @@
             .name = "tls-port",
             .type = QEMU_OPT_NUMBER,
         },{
+            .name = "addr",
+            .type = QEMU_OPT_STRING,
+        },{
+            .name = "ipv4",
+            .type = QEMU_OPT_BOOL,
+        },{
+            .name = "ipv6",
+            .type = QEMU_OPT_BOOL,
+        },{
             .name = "password",
             .type = QEMU_OPT_STRING,
         },{