Strip brackets from vnc host

Commit v2.2.0-1530-ge5560329 vnc: switch to inet_listen_opts
bypassed the use of inet_parse in inet_listen, making literal
IPv6 addresses enclosed in brackets fail:

qemu-kvm: -vnc [::1]:0: Failed to start VNC server on `(null)': address
resolution failed for [::1]:5900: Name or service not known

Strip the brackets to make it work again.
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/vnc.c

@@ -3482,7 +3482,14 @@ void vnc_display_open(const char *id, Error **errp)
 
     h = strrchr(vnc, ':');
     if (h) {
-        char *host = g_strndup(vnc, h - vnc);
+        char *host;
+        size_t hlen = h - vnc;
+
+        if (vnc[0] == '[' && vnc[hlen - 1] == ']') {
+            host = g_strndup(vnc + 1, hlen - 2);
+        } else {
+            host = g_strndup(vnc, hlen);
+        }
         qemu_opt_set(sopts, "host", host, &error_abort);
         qemu_opt_set(wsopts, "host", host, &error_abort);
         qemu_opt_set(sopts, "port", h+1, &error_abort);