Rename IPC_M_DATA_SEND to IPC_M_DATA_WRITE. Now, when we also add
IPC_M_DATA_READ, it will not clash and cause confusion with userspace wrappers
such as ipc_data_receive(). Rename the forementioned wrappers to
ipc_data_write_send(), ipc_data_write_receive() and ipc_data_write_deliver().