udev: input_id: tag pointing sticks as ID_INPUT_POINTINGSTICK

Also referred to as trackpoint, trackstick. These are marked by recent kernels
through an input prop. Forward that prop as udev property so userspace can
easily determine whether there is a pointing stick present.

These devices were previously marked as ID_INPUT_MOUSE, for backwards
compatibility we keep that in place, the new property is an addition.

src/shared/missing.h

@@ -948,3 +948,7 @@ static inline int kcmp(pid_t pid1, pid_t pid2, int type, unsigned long idx1, uns
 #ifndef KCMP_FILE
 #define KCMP_FILE 0
 #endif
+
+#ifndef INPUT_PROP_POINTING_STICK
+#define INPUT_PROP_POINTING_STICK 0x05
+#endif