sctp: add sysctl net.sctp.l3mdev_accept

This patch is to add sysctl net.sctp.l3mdev_accept to allow
users to change the pernet global l3mdev_accept.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.rst

@@ -3127,6 +3127,15 @@ ecn_enable - BOOLEAN
 
         Default: 1
 
+l3mdev_accept - BOOLEAN
+	Enabling this option allows a "global" bound socket to work
+	across L3 master domains (e.g., VRFs) with packets capable of
+	being received regardless of the L3 domain in which they
+	originated. Only valid when the kernel was compiled with
+	CONFIG_NET_L3_MASTER_DEV.
+
+	Default: 1 (enabled)
+
 
 ``/proc/sys/net/core/*``
 ========================

net/sctp/sysctl.c

@@ -347,6 +347,17 @@ static struct ctl_table sctp_net_table[] = {
 		.extra1		= &max_autoclose_min,
 		.extra2		= &max_autoclose_max,
 	},
+#ifdef CONFIG_NET_L3_MASTER_DEV
+	{
+		.procname	= "l3mdev_accept",
+		.data		= &init_net.sctp.l3mdev_accept,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
+	},
+#endif
 	{
 		.procname	= "pf_enable",
 		.data		= &init_net.sctp.pf_enable,