Move memset() from net_client_uninit() to net_client_init()

zeroing a structure before using it is more common than zeroing after
using it. Also makes the setting of nd->used more obvious.
Signed-off-by: NMark McLoughlin <markmc@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

net.c

@@ -2443,6 +2443,7 @@ int net_client_init(Monitor *mon, const char *device, const char *p)
             goto out;
         }
         nd = &nd_table[idx];
+        memset(nd, 0, sizeof(*nd));
         macaddr = nd->macaddr;
         macaddr[0] = 0x52;
         macaddr[1] = 0x54;
@@ -2818,7 +2819,7 @@ void net_client_uninit(NICInfo *nd)
     qemu_free(nd->devaddr);
     qemu_free(nd->id);
 
-    memset(nd, 0, sizeof(*nd));
+    nd->used = 0;
 }
 
 static int net_host_check_device(const char *device)