From core/include/msg.h:

/**
 * @brief Initialize the current thread's message queue.
 *
 * @param[in] array Pointer to preallocated array of ``msg_t`` structures, must
 *                  not be NULL.
 * @param[in] num   Number of ``msg_t`` structures in array.
 *                  **MUST BE POWER OF TWO!**
 *
 * @return 0, if successful
 * @return -1, on error
 */
int msg_init_queue(msg_t *array, int num);

sizeof(array) does does not compute an array size. Replace calls to sizeof()
with proper values

Closes #3269.

Fix two crashes in the tests and probably more in the network stack.