[PATCH pve-network] sdn: controller: fallback to interface mac if no master

[Hannes Laimer <h.laimer@proxmox.com>]

For IPv6 underlays, we can't directly use the IP for the router-id.
Therefore, `get_router_id` derives a unique ID from the last 4 bytes of
the interface MAC.

However, the current MAC retrieval logic only checks the master device.
This fails for standalone interfaces that do not have a master, such as
`dummy_` interfaces used for fabrics.

Update `read_iface_mac` to fall back to the interface's own address if
no master address is found.

Signed-off-by: Hannes Laimer <h.laimer@proxmox.com>
---
 src/PVE/Network/SDN/Controllers/Plugin.pm | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/PVE/Network/SDN/Controllers/Plugin.pm b/src/PVE/Network/SDN/Controllers/Plugin.pm
index d70e518..cab036a 100644
--- a/src/PVE/Network/SDN/Controllers/Plugin.pm
+++ b/src/PVE/Network/SDN/Controllers/Plugin.pm
@@ -105,7 +105,9 @@ sub on_update_hook {
 
 sub read_iface_mac {
     my ($iface) = @_;
-    return PVE::Tools::file_read_firstline("/sys/class/net/$iface/master/address");
+    my $mac = PVE::Tools::file_read_firstline("/sys/class/net/$iface/master/address");
+    return $mac if $mac;
+    return PVE::Tools::file_read_firstline("/sys/class/net/$iface/address");
 }
 
 sub get_router_id {
-- 
2.47.3