Since application callbacks happen from the rx thread we cannot have
the stack as small as just 256 bytes. Make it 2kB for now, but later
this needs to be adjusted to some reasonable minimum with the help of
the stack analysis code, and then probably accompanied by a Kconfig
option for apps to increase if if needed.
Change-Id: Ie8e2ac41701101b874378ded1435a6fb06bae497
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>