Bluetooth: Increase stack size to default value

Make stack size the same size as in hello app. Current stack cannot
handle correctly security tests.

Change-Id: I5946c6bbcbc5079cefefddbb229b3205364b24d0
Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>

samples/bluetooth/shell/src/btshell.c

@@ -64,7 +64,7 @@ static const char *prompt;
 static char *argv[ARGC_MAX + 1];
 static size_t argc;
 
-#define STACKSIZE 512
+#define STACKSIZE 2000
 static char __stack stack[STACKSIZE];
 
 #define MAX_CMD_QUEUED 3