Rename frame elements with c-style names

[jonnew]

The components of a frame in the hardware spec:

ONI/source/hw-spec/controller/channels/data_frames.rst

Lines 10 to 18 in 7649f1d

	The frame format is:
	::
	uint32 Device_Address
	uint64 Common_Timestamp
	uint32 Sample_Size
	var Sample

should be renamed (and all references as well) with c-style names that better reflect what they are. e.g.

The frame format is:

::

    uint32  dev_addr
    uint64  acqclk_cnt
    uint32  sample_sz
    var     sample

[jonnew]

This will require a document-level review for consistency.