Shanling Q2 port v2.6

• Fixes Bluetooth playback, broken in v2.5. Headphone jack detection was read inverted, so empty jacks counted as headphones plugged in and Rockbox played to the DAC instead of a connected Bluetooth headset. Wired headphones still win over Bluetooth, and plugging them in while playing over Bluetooth switches to them.
• Pause on headphone unplug now fires on unplugging rather than on plugging in.

Install by unzipping rockbox.zip over .rockbox on the card; your config.cfg is kept.