Added route(..), fixed dap_enable(..)

Adding route() made me review dap_enable() more closely and it wasn't
doing what I intended to do before, it was ignoring I2S coming back from
Teensy, DAP was sourced from ADC as was I2S_DOUT and DAC was sourced
from DAP; Teensy received valid data from ADC but data from Teensy was
just discarded if user enabled dap previously.

Paul, please test this update before accepting the pull request.

I nearly renamed dap_enable to audioProcessorEnable just because I was touching it but decided to hold off on that till I sit to work on the bigger overhaul soon enough; family may be about to jump me to pay them attention and I want to work on my current pet project a bit too so...