default.pa: Load module-jackdbus-detect with channels=2 by default

default.pa: Load module-jackdbus-detect with channels=2 by default

There was a recent thread on Linux Audio Users mailinglist about
whether to do so or not, and it looks like most people would prefer
having a stereo default (but even better would have been a
module-jack-card where you can easily set channels/profiles on the fly).

Reference:
http://lists.linuxaudio.org/pipermail/linux-audio-user/2013-February/091068.html

Reported-by: Kaj Ailomaa <zequence@mousike.me>
Signed-off-by: David Henningsson <david.henningsson@canonical.com>