[PATCH net-next v2] docs: net: document neigh gc_stale_time sysctl

[Gabriel Goller <g.goller@proxmox.com>]

Add missing documentation for a neighbor table garbage collector sysctl
parameter in ip-sysctl.rst:

neigh/default/gc_stale_time: controls how long an unused neighbor entry
is kept before becoming eligible for garbage collection (default: 60
seconds)

Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
---

Changelog:
v1:
 * removed documentation for gc_interval, as that sysctl is not used
   anymore and doesn't do anything.
 * mention gc_stale_time only being used when we have more than
   gc_thresh1 neighbors.

 Documentation/networking/ip-sysctl.rst | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 28c7e4f5ecf9..85fda3759534 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -202,6 +202,17 @@ neigh/default/gc_thresh3 - INTEGER
 
 	Default: 1024
 
+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
+	not been used for longer than this time will be removed by the garbage
+	collector, unless they have active references, are marked as PERMANENT,
+	or carry the NTF_EXT_LEARNED or NTF_EXT_VALIDATED flag. Stale entries
+	are only removed by the periodic GC when there are at least gc_thresh1
+	neighbors in the table.
+
+	Default: 60 seconds
+
 neigh/default/unres_qlen_bytes - INTEGER
 	The maximum number of bytes which may be used by packets
 	queued for each	unresolved address by other network layers.
-- 
2.47.3