Correct MAXUID

The uid_t on most systems is in fact and unsigned 32-bit value.
This is almost always correct, however you could compile your
kernel to use an unsigned 16-bit value for uid_t.  In practice
I've never encountered a distribution which does this so I'm
willing to overlook this corner case for now.

include/sys/param.h

@@ -31,6 +31,6 @@
 #define ptob(pages)			(pages << PAGE_SHIFT)
 #define btop(bytes)			(bytes >> PAGE_SHIFT)
 
-#define MAXUID				2147483647
+#define MAXUID				UINT32_MAX
 
 #endif /* SPL_PARAM_H */