Fix up r299764

I meant to use nitems, not sizeof(..) with the destination buffer. Using sizeof(..)
on a pointer will always truncate the output in the destination buffer incorrectly

Pointyhat to: ngie
MFC after: 1 week
X-MFC with: r299764
Sponsored by: EMC / Isilon Storage Division

usr.sbin/bsnmpd/tools/libbsnmptools/bsnmptools.c

@@ -264,7 +264,7 @@ add_filename(struct snmp_toolinfo *snmptoolctx, const char *filename,
 
 	if (cut != NULL)
 		asn_append_oid(&(entry->cut), cut);
-	strlcpy(fstring, filename, sizeof(fstring));
+	strlcpy(fstring, filename, nitems(fstring));
 	entry->name = fstring;
 	entry->done = done;
 	SLIST_INSERT_HEAD(&snmptoolctx->filelist, entry, link);