Add little/big endian check

[ghost]

This will use the system little/big endian status to set the value of endianness in rosimagesrc_set_msg_props_from_caps_string(). It's slightly better than just guessing.

[BrettRD]

Thanks for flagging that!

looking through the format enums gstreamer knows of, many of them can specify the endianness there.
The format enum should have a good idea of what the caps endianness is, that allows the user to specify the endianness in a caps string and then run a big-endian stream on a little-endian machine.

gst_video_format_get_info can unpack the enum into a data structure, GST_VIDEO_FORMAT_INFO_IS_LE will check if the caps is little endian.

That would save us from having to test behaviour of undefined operations

[ghost]

Good catch. Will resubmit patch to use that.