audiotrack: add an option for maximum number of channels
audiotrack: add an option for maximum number of channels

Android mediaserver crashes when you output 5.1 PCM @48kHz via Audiotrack with
a lot of QCOM devices due to a SIGSEGV in their resampler. It happens with
Samsung Galaxy Tab 3/4, Galaxy S4/S5 and many other devices.

Therefore, activate surround only via an extra option.

Signed-off-by: Jean-Baptiste Kempf <7b85a41a628204b76aba4326273a3ccc74bd009a@videolan.org>

shyamalschandra/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,krichter722/vlc,shyamalschandra/vlc,xkfz007/vlc,xkfz007/vlc,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,shyamalschandra/vlc,xkfz007/vlc,vlc-mirror/vlc,krichter722/vlc,shyamalschandra/vlc,xkfz007/vlc,krichter722/vlc,krichter722/vlc,vlc-mirror/vlc,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,vlc-mirror/vlc,shyamalschandra/vlc,krichter722/vlc