Include sys/types.h here

It's included by header pollution in most of the compile
environments. However, in the standalone envirnment, it's not
included. Go ahead and include it always since the overhead is low and
it is simpler that way.

MFC After: 3 days

sys/opencrypto/xform_aes_xts.c

@@ -50,6 +50,7 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <sys/types.h>
 #include <opencrypto/xform_enc.h>
 
 static	int aes_xts_setkey(void *, const uint8_t *, int);