fixed arguments of socket functions to match the standard; converted size argument of netconn_write to 'size_t' for that; fixed some warnings

src/api/api_lib.c

@@ -459,7 +459,7 @@ netconn_send(struct netconn *conn, struct netbuf *buf)
  * @return ERR_OK if data was sent, any other err_t on error
  */
 err_t
-netconn_write(struct netconn *conn, const void *dataptr, int size, u8_t apiflags)
+netconn_write(struct netconn *conn, const void *dataptr, size_t size, u8_t apiflags)
 {
   struct api_msg msg;