vxlan: Refresh FDB 'updated' time upon user space updates

When a host migrates to a different remote and a packet is received from
the new remote, the corresponding FDB entry is updated and its 'updated'
time is refreshed.

However, when user space replaces the remote of an FDB entry, its
'updated' time is not refreshed:

 # ip link add name vx1 up type vxlan id 10010 dstport 4789
 # bridge fdb add 00:11:22:33:44:55 dev vx1 self dynamic dst 198.51.100.1
 # sleep 10
 # bridge -s -j -p fdb get 00:11:22:33:44:55 br vx1 self | jq '.[]["updated"]'
 10
 # bridge fdb replace 00:11:22:33:44:55 dev vx1 self dynamic dst 198.51.100.2
 # bridge -s -j -p fdb get 00:11:22:33:44:55 br vx1 self | jq '.[]["updated"]'
 10

This can lead to the entry being aged out prematurely and it is also
inconsistent with the bridge driver:

 # ip link add name br1 up type bridge
 # ip link add name swp1 master br1 up type dummy
 # ip link add name swp2 master br1 up type dummy
 # bridge fdb add 00:11:22:33:44:55 dev swp1 master dynamic vlan 1
 # sleep 10
 # bridge -s -j fdb get 00:11:22:33:44:55 br br1 vlan 1 | jq '.[]["updated"]'
 10
 # bridge fdb replace 00:11:22:33:44:55 dev swp2 master dynamic vlan 1
 # bridge -s -j fdb get 00:11:22:33:44:55 br br1 vlan 1 | jq '.[]["updated"]'
 0

Adjust the VXLAN driver to refresh the 'updated' time of an FDB entry
whenever one of its attributes is changed by user space:

 # ip link add name vx1 up type vxlan id 10010 dstport 4789
 # bridge fdb add 00:11:22:33:44:55 dev vx1 self dynamic dst 198.51.100.1
 # sleep 10
 # bridge -s -j -p fdb get 00:11:22:33:44:55 br vx1 self | jq '.[]["updated"]'
 10
 # bridge fdb replace 00:11:22:33:44:55 dev vx1 self dynamic dst 198.51.100.2
 # bridge -s -j -p fdb get 00:11:22:33:44:55 br vx1 self | jq '.[]["updated"]'
 0

Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://patch.msgid.link/20250204145549.1216254-6-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/vxlan/vxlan_core.c

@@ -1013,12 +1013,10 @@ static int vxlan_fdb_update_existing(struct vxlan_dev *vxlan,
 	    !(f->flags & NTF_VXLAN_ADDED_BY_USER)) {
 		if (f->state != state) {
 			f->state = state;
-			WRITE_ONCE(f->updated, jiffies);
 			notify = 1;
 		}
 		if (f->flags != fdb_flags) {
 			f->flags = fdb_flags;
-			WRITE_ONCE(f->updated, jiffies);
 			notify = 1;
 		}
 	}
@@ -1060,6 +1058,7 @@ static int vxlan_fdb_update_existing(struct vxlan_dev *vxlan,
 		if (rd == NULL)
 			rd = first_remote_rtnl(f);
 
+		WRITE_ONCE(f->updated, jiffies);
 		err = vxlan_fdb_notify(vxlan, f, rd, RTM_NEWNEIGH,
 				       swdev_notify, extack);
 		if (err)