Feature: Ability for zalsa to auto detect quantity of channels

[riban-bw]

The jack tools alsa_in and alsa_out will automatically detect the quantity of audio channels on a card if the -c parameter is not passed. zalsa requires the quantity of channels to be explicitly defined, defaulting to 2 if not. For backwards compatibility with alsa_in/out and to simplify use, it would be advantageous for zalsa to detect the quantity of audio channels if -c option is not provided.