Bluetooth: Use sizeof() for stack when starting fibers

In case there are changes to the way the stacks are defined it's safer
to use sizeof() rather than rely on some specific size define.

Change-Id: Ic9ae090c0dbc0d88995a8883f9b4876be5958f1d
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
1 file changed