net: fix multiple NICs causing net opts process to stop

For NICs, net_init_client() returns the index into the NICInfo table.

qemu_opts_foreach() interprets non-zero as an error return an stops
iterating over the options.

So, if you have more than one '-net nic' on the command line, subsequent
'-net' options do not get processed.

Fix this by making net_client_init() only return non-zero if
net_init_client() returns an error.
Reported-by: NPeter Lieven <pl@dlh.net>
Patchworks-ID: 35736
Signed-off-by: NMark McLoughlin <markmc@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

net.c

@@ -3302,7 +3302,9 @@ static void net_check_clients(void)
 
 static int net_init_client(QemuOpts *opts, void *dummy)
 {
-    return net_client_init(NULL, opts, 0);
+    if (net_client_init(NULL, opts, 0) < 0)
+        return -1;
+    return 0;
 }
 
 static int net_init_netdev(QemuOpts *opts, void *dummy)