kern_sysctl: make sysctl.debug work as intended

r136999 introduced SYSTCL_DEBUG but apparently "opt_sysctl.h" was never
included making the option ignored.

r322954 introduced sysctl.reuse_test with OID number equal to 0, effectively
shadowing the very special sysctl.debug one. Use OID_AUTO as it doesn't need
any special treatment.

Reviewed by:	kib (mentor)
Approved by:	kib (mentor)
Differential Revision:	https://reviews.freebsd.org/D23056

sys/kern/kern_sysctl.c

@@ -43,6 +43,7 @@ __FBSDID("$FreeBSD$");
 #include "opt_capsicum.h"
 #include "opt_ddb.h"
 #include "opt_ktrace.h"
+#include "opt_sysctl.h"
 
 #include <sys/param.h>
 #include <sys/fail.h>
@@ -404,8 +405,9 @@ sysctl_reuse_test(SYSCTL_HANDLER_ARGS)
 	SYSCTL_RUNLOCK(&tracker);
 	return (0);
 }
-SYSCTL_PROC(_sysctl, 0, reuse_test, CTLTYPE_STRING|CTLFLAG_RD|CTLFLAG_MPSAFE,
-	0, 0, sysctl_reuse_test, "-", "");
+SYSCTL_PROC(_sysctl, OID_AUTO, reuse_test,
+    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, 0, 0, sysctl_reuse_test, "-",
+    "");
 #endif
 
 void