brymen-dmm: rephrase bfunc and value text parsing

brymen-dmm: rephrase bfunc and value text parsing

When the BM850s response packet's payload gets interpreted, the DLE/STX
transport envelope is not of interest. Rephrase the bitfield inspection
to better reflect that 'bfunc' indicators get accessed (match the vendor's
documentation). Rephrase the calling parse routine to unobfuscate the text
field access. Unclutter assignments for the analog feed. Use a shorter
layout in debug messages, reflect raw input data and conversion results.