net: context: Allow to put context into FIFO at expense of user_data

By moving user_data member at the beginning of structure. With
refcount at the beginning, reliable passsing of contexts via
FIFO was just impossible. (Queuing contexts to a FIFO is required
for BSD Sockets API).

Signed-off-by: Paul Sokolovsky <[email protected]>

Author: pfalcon

include/net/net_context.h

@@ -176,6 +176,13 @@ struct net_conn_handle;
  * anyway. This saves 12 bytes / context in IPv6.
  */
 struct net_context {
+	/** User data.
+	 *
+	 *  First member of the structure to let users either have user data
+	 *  associated with a context, or put contexts into a FIFO.
+	 */
+	void *user_data;
+
 	/** Reference count
 	 */
 	atomic_t refcount;
@@ -206,10 +213,6 @@ struct net_context {
 	 */
 	net_context_connect_cb_t connect_cb;
 
-	/** User data.
-	 */
-	void *user_data;
-
 #if defined(CONFIG_NET_CONTEXT_NET_PKT_POOL)
 	/** Get TX net_buf pool for this context.
 	 */