Zephyr port: unnecessary flash alignment check

[sw]

This relates to apache/mynewt-newtmgr#185

There is a performance problem when using mcumgr CLI to upload firmware images to a Zephyr system. There is an overhead of up to 4x in the data transmitted on the serial port.

On the one hand, this is due to sub-optimal frame handling in mcumgr CLI as reported in apache/mynewt-newtmgr#185

But I suspect the MCU side could also be improved.

img_mgmt_impl_upload_inspect rounds the data length down to a multiple of the flash write block size:

mynewt-mcumgr/cmd/img_mgmt/port/zephyr/src/zephyr_img_mgmt.c

Lines 571 to 576 in 798f7fe

	rem_bytes = req->data_len % flash_area_align(fa);
	flash_area_close(fa);
	if (rem_bytes) {
	action->write_bytes -= rem_bytes;
	}

But then, buffered write is used in img_mgmt_impl_write_image_data:

mynewt-mcumgr/cmd/img_mgmt/port/zephyr/src/zephyr_img_mgmt.c

Line 307 in 798f7fe

rc = flash_img_buffered_write(ctx, (void *)data, num_bytes, last);

According to the documentation of flash_img_buffered_write, this function will store non-complete blocks in RAM until it is called with flush == true. So a length that is not a multiple of the flash write block size should not pose a problem.

My suggestion would be to remove the length truncation in img_mgmt_impl_upload_inspect.
Or is there some special case that this would break?