Add entry for the neigh/default/gc_interval sysctl. This sysctl is
unused since kernel v2.6.8.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
---
 Documentation/networking/ip-sysctl.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index d1eeb5323af0..265158534cda 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -202,6 +202,13 @@ neigh/default/gc_thresh3 - INTEGER
 
 	Default: 1024
 
+neigh/default/gc_interval - INTEGER
+	Specifies how often the garbage collector for neighbor entries
+	should run. This value applies to the entire table, not
+	individual entries. Unused since kernel v2.6.8.
+
+	Default: 30 seconds
+
 neigh/default/gc_stale_time - INTEGER
 	Determines how long a neighbor entry can remain unused before it is
 	considered stale and eligible for garbage collection. Entries that have
-- 
2.47.3