net: Fix '-net nic,model=' for non-help arguments

Oops, don't *delete* the model option when checking for 'help'.

Fixes: 64f75f57f9 ("net: Reinstate '-net nic, model=help' output as documented in man page")
Reported-by: Hans <sungdgdhtryrt@gmail.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Cc: qemu-stable@nongnu.org
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/net.c

@@ -1737,7 +1737,7 @@ void net_check_clients(void)
 
 static int net_init_client(void *dummy, QemuOpts *opts, Error **errp)
 {
-    const char *model = qemu_opt_get_del(opts, "model");
+    const char *model = qemu_opt_get(opts, "model");
 
     if (is_nic_model_help_option(model)) {
         return 0;