Define u_int in libnfs-zdr.h for mingw again

The typedef for u_int was removed in 172f46756e,
assuming that sys/types.h defines it. This doesn't seam to be the case on mingw.

include/nfsc/libnfs-zdr.h

@@ -92,6 +92,9 @@ struct ZDR {
 typedef struct ZDR ZDR;
 
 
+#ifdef __MINGW32__
+typedef uint32_t u_int;
+#endif
 typedef uint32_t enum_t;
 typedef uint32_t bool_t;