net: introduce NetClientState destructor

To allow allocating an array of NetClientState and free it once, this patch
introduces destructor of NetClientState. Which could do type specific free,
which could be used by multiqueue to free the array once.
Signed-off-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

include/net/net.h

@@ -35,6 +35,7 @@ typedef ssize_t (NetReceive)(NetClientState *, const uint8_t *, size_t);
 typedef ssize_t (NetReceiveIOV)(NetClientState *, const struct iovec *, int);
 typedef void (NetCleanup) (NetClientState *);
 typedef void (LinkStatusChanged)(NetClientState *);
+typedef void (NetClientDestructor)(NetClientState *);
 
 typedef struct NetClientInfo {
     NetClientOptionsKind type;
@@ -58,6 +59,7 @@ struct NetClientState {
     char *name;
     char info_str[256];
     unsigned receive_disabled : 1;
+    NetClientDestructor *destructor;
 };
 
 typedef struct NICState {

net/net.c

@@ -182,11 +182,17 @@ static char *assign_name(NetClientState *nc1, const char *model)
     return g_strdup(buf);
 }
 
+static void qemu_net_client_destructor(NetClientState *nc)
+{
+    g_free(nc);
+}
+
 static void qemu_net_client_setup(NetClientState *nc,
                                   NetClientInfo *info,
                                   NetClientState *peer,
                                   const char *model,
-                                  const char *name)
+                                  const char *name,
+                                  NetClientDestructor *destructor)
 {
     nc->info = info;
     nc->model = g_strdup(model);
@@ -204,7 +210,7 @@ static void qemu_net_client_setup(NetClientState *nc,
     QTAILQ_INSERT_TAIL(&net_clients, nc, next);
 
     nc->send_queue = qemu_new_net_queue(nc);
-
+    nc->destructor = destructor;
 }
 
 NetClientState *qemu_new_net_client(NetClientInfo *info,
@@ -217,7 +223,8 @@ NetClientState *qemu_new_net_client(NetClientInfo *info,
     assert(info->size >= sizeof(NetClientState));
 
     nc = g_malloc0(info->size);
-    qemu_net_client_setup(nc, info, peer, model, name);
+    qemu_net_client_setup(nc, info, peer, model, name,
+                          qemu_net_client_destructor);
 
     return nc;
 }
@@ -279,7 +286,9 @@ static void qemu_free_net_client(NetClientState *nc)
     }
     g_free(nc->name);
     g_free(nc->model);
-    g_free(nc);
+    if (nc->destructor) {
+        nc->destructor(nc);
+    }
 }
 
 void qemu_del_net_client(NetClientState *nc)