Read-only access from sysctl(2) interface.

Index: sys/netinet/ip_input.c
===================================================================
RCS file: /cvs/src/sys/netinet/ip_input.c,v
diff -u -p -r1.411 ip_input.c
--- sys/netinet/ip_input.c	23 Jun 2025 09:16:32 -0000	1.411
+++ sys/netinet/ip_input.c	23 Jun 2025 13:12:21 -0000
@@ -116,12 +116,12 @@ const struct sysctl_bounded_args ipctl_v
 	{ IPCTL_FORWARDING, &ip_forwarding, 0, 2 },
 	{ IPCTL_SENDREDIRECTS, &ip_sendredirects, 0, 1 },
 	{ IPCTL_DIRECTEDBCAST, &ip_directedbcast, 0, 1 },
-};
-
-const struct sysctl_bounded_args ipctl_vars[] = {
 #ifdef MROUTING
 	{ IPCTL_MRTPROTO, &ip_mrtproto, SYSCTL_INT_READONLY },
 #endif
+};
+
+const struct sysctl_bounded_args ipctl_vars[] = {
 	{ IPCTL_DEFTTL, &ip_defttl, 0, 255 },
 	{ IPCTL_IPPORT_FIRSTAUTO, &ipport_firstauto, 0, 65535 },
 	{ IPCTL_IPPORT_LASTAUTO, &ipport_lastauto, 0, 65535 },
@@ -1830,6 +1830,9 @@ ip_sysctl(int *name, u_int namelen, void
 	case IPCTL_FORWARDING:
 	case IPCTL_SENDREDIRECTS:
 	case IPCTL_DIRECTEDBCAST:
+#ifdef MROUTING
+	case IPCTL_MRTPROTO:
+#endif
 		return (sysctl_bounded_arr(
 		    ipctl_vars_unlocked, nitems(ipctl_vars_unlocked),
 		    name, namelen, oldp, oldlenp, newp, newlen));