tests: fix wrong interface name in SRv6 topotest

Previously, routes leaked from one VRF to another VRF were associated
with the original nexthop interface.

5051dd3d0 ("bgpd: fix invalid nexthop interface on leaked routes")
replaced the nexthop interface with the index of incoming VRF interface.

Due to this change, the `bgp_srv6l3vpn_route_leak` topotest always fails
because it still expects the nexthop interface.

This commit fixes the expected interface name in the
`bgp_srv6l3vpn_route_leak` topotest.

Signed-off-by: Carmine Scarpitta <[email protected]>
Signed-off-by: Louis Scalbert <[email protected]>

tests/topotests/bgp_srv6l3vpn_route_leak/pe1/results/vrf20_ipv4.json

@@ -12,7 +12,7 @@
                 {
                     "fib": true,
                     "directlyConnected": true,
-                    "interfaceName": "eth0",
+                    "interfaceName": "vrf10",
                     "vrf": "vrf10",
                     "active": true
                 }