Both usage paths of ip6_forward() are dead ends. We don't need to cache
value.

IPV6CTL_LOG_INTERVAL is also unused by ramdisk.

Index: sys/netinet6/in6_proto.c
===================================================================
RCS file: /cvs/src/sys/netinet6/in6_proto.c,v
diff -u -p -r1.137 in6_proto.c
--- sys/netinet6/in6_proto.c	21 Jul 2025 11:07:31 -0000	1.137
+++ sys/netinet6/in6_proto.c	21 Jul 2025 12:03:21 -0000
@@ -356,7 +356,7 @@ int	ip6_defhlim = IPV6_DEFHLIM;	/* [a] *
 int	ip6_defmcasthlim = IPV6_DEFAULT_MULTICAST_HOPS;
 int	ip6_maxfragpackets = 200;	/* [a] */
 int	ip6_maxfrags = 200;
-int	ip6_log_interval = 5;
+int	ip6_log_interval = 5;	/* [a] */
 int	ip6_hdrnestlimit = 10;	/* appropriate? */
 int	ip6_dad_count = 1;	/* DupAddrDetectionTransmits */
 int	ip6_dad_pending;	/* number of currently running DADs */
Index: sys/netinet6/ip6_forward.c
===================================================================
RCS file: /cvs/src/sys/netinet6/ip6_forward.c,v
diff -u -p -r1.127 ip6_forward.c
--- sys/netinet6/ip6_forward.c	8 Jul 2025 00:47:41 -0000	1.127
+++ sys/netinet6/ip6_forward.c	21 Jul 2025 12:03:21 -0000
@@ -110,7 +110,8 @@ ip6_forward(struct mbuf *m, struct route
 		ip6stat_inc(ip6s_cantforward);
 		uptime = getuptime();
 
-		if (ip6_log_time + ip6_log_interval < uptime) {
+		if (ip6_log_time + atomic_load_int(&ip6_log_interval) <
+		    uptime) {
 			ip6_log_time = uptime;
 			inet_ntop(AF_INET6, &ip6->ip6_src, src6, sizeof(src6));
 			inet_ntop(AF_INET6, &ip6->ip6_dst, dst6, sizeof(dst6));
@@ -227,7 +228,8 @@ reroute:
 		ip6stat_inc(ip6s_badscope);
 		uptime = getuptime();
 
-		if (ip6_log_time + ip6_log_interval < uptime) {
+		if (ip6_log_time + atomic_load_int(&ip6_log_interval) <
+		    uptime) {
 			ip6_log_time = uptime;
 			inet_ntop(AF_INET6, &ip6->ip6_src, src6, sizeof(src6));
 			inet_ntop(AF_INET6, &ip6->ip6_dst, dst6, sizeof(dst6));
Index: sys/netinet6/ip6_input.c
===================================================================
RCS file: /cvs/src/sys/netinet6/ip6_input.c,v
diff -u -p -r1.281 ip6_input.c
--- sys/netinet6/ip6_input.c	21 Jul 2025 11:07:31 -0000	1.281
+++ sys/netinet6/ip6_input.c	21 Jul 2025 12:03:21 -0000
@@ -1448,10 +1448,10 @@ const struct sysctl_bounded_args ipv6ctl
 #endif
 	{ IPV6CTL_DEFHLIM, &ip6_defhlim, 0, 255 },
 	{ IPV6CTL_MAXFRAGPACKETS, &ip6_maxfragpackets, 0, 1000 },
+	{ IPV6CTL_LOG_INTERVAL, &ip6_log_interval, 0, INT_MAX },
 };
 
 const struct sysctl_bounded_args ipv6ctl_vars[] = {
-	{ IPV6CTL_LOG_INTERVAL, &ip6_log_interval, 0, INT_MAX },
 	{ IPV6CTL_HDRNESTLIMIT, &ip6_hdrnestlimit, 0, 100 },
 	{ IPV6CTL_DAD_COUNT, &ip6_dad_count, 0, 10 },
 	{ IPV6CTL_AUTO_FLOWLABEL, &ip6_auto_flowlabel, 0, 1 },
@@ -1571,6 +1571,7 @@ ip6_sysctl(int *name, u_int namelen, voi
 #endif
 	case IPV6CTL_DEFHLIM:
 	case IPV6CTL_MAXFRAGPACKETS:
+	case IPV6CTL_LOG_INTERVAL:
 		return (sysctl_bounded_arr(
 		    ipv6ctl_vars_unlocked, nitems(ipv6ctl_vars_unlocked),
 		    name, namelen, oldp, oldlenp, newp, newlen));
Index: sys/netinet6/ip6_mroute.c
===================================================================
RCS file: /cvs/src/sys/netinet6/ip6_mroute.c,v
diff -u -p -r1.150 ip6_mroute.c
--- sys/netinet6/ip6_mroute.c	8 Jul 2025 00:47:41 -0000	1.150
+++ sys/netinet6/ip6_mroute.c	21 Jul 2025 12:03:21 -0000
@@ -923,7 +923,8 @@ ip6_mforward(struct ip6_hdr *ip6, struct
 	 */
 	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
 		ip6stat_inc(ip6s_cantforward);
-		if (ip6_log_time + ip6_log_interval < getuptime()) {
+		if (ip6_log_time + atomic_load_int(&ip6_log_interval) <
+		    getuptime()) {
 			char src[INET6_ADDRSTRLEN], dst[INET6_ADDRSTRLEN];
 
 			ip6_log_time = getuptime();