Enable sys/random.h #include from C++

And bump __FreeBSD_version, just in case.

PR:		234180
Submitted by:	Ralf van der Enden <tremere AT cainites.net>
MFC after:	5 days

sys/sys/param.h

@@ -60,7 +60,7 @@
  *		in the range 5 to 9.
  */
 #undef __FreeBSD_version
-#define __FreeBSD_version 1300005	/* Master, propagated to newvers */
+#define __FreeBSD_version 1300006	/* Master, propagated to newvers */
 
 /*
  * __FreeBSD_kernel__ indicates that this system uses the kernel of FreeBSD,

sys/sys/random.h

@@ -153,6 +153,9 @@ void random_harvest_deregister_source(enum random_entropy_source);
 
 #define GRND_NONBLOCK	0x1
 #define GRND_RANDOM	0x2
+
+__BEGIN_DECLS
 ssize_t getrandom(void *buf, size_t buflen, unsigned int flags);
+__END_DECLS
 
 #endif /* _SYS_RANDOM_H_ */