BSD.root.dist: Correct tag for /etc/sysctl.kld.d

This is only used by rc.subr and belongs in rc, not runtime.

Fixes:		fa6d67cd16 ("BSD.root.dist: Add package tag for all directories")
MFC after:	3 days
Reviewed by:	ivy
Differential Revision:	https://reviews.freebsd.org/D56900

etc/mtree/BSD.root.dist

@@ -105,7 +105,7 @@
             untrusted		tags=package=caroot
             ..
         ..
-        sysctl.kld.d    tags=package=runtime
+        sysctl.kld.d    tags=package=rc
         ..
         syslog.d        tags=package=syslogd
         ..