fib: Don't back walk from a path-list when a child fist attaches.

Type: fix

If the walk is triggered when the child is added, then that child is visited in the walk. However, since it is just attahcing to the path-list it may not, or indeed cannot, have all the context it needs to successfully handle the walk.
In the case of MPLS tunnel, it does not have the path extensions ready, and cannot since the path extensions need to resolve on the path-list.

Signed-off-by: Neale Ranns <neale@graphiant.com>
Change-Id: I027af8cf2f522d2f6e37931bea60c767f0cb667d
diff --git a/test/test_mpls.py b/test/test_mpls.py
index 2c40e8d..2b959e4 100644
--- a/test/test_mpls.py
+++ b/test/test_mpls.py
@@ -1069,7 +1069,7 @@
     def test_mpls_tunnel_many(self):
         """ MPLS Multiple Tunnels """
 
-        for ii in range(10):
+        for ii in range(100):
             mpls_tun = VppMPLSTunnelInterface(
                 self,
                 [VppRoutePath(self.pg0.remote_ip4,
@@ -1078,6 +1078,16 @@
                                       VppMplsLabel(46, MplsLspMode.UNIFORM)])])
             mpls_tun.add_vpp_config()
             mpls_tun.admin_up()
+        for ii in range(100):
+            mpls_tun = VppMPLSTunnelInterface(
+                self,
+                [VppRoutePath(self.pg0.remote_ip4,
+                              self.pg0.sw_if_index,
+                              labels=[VppMplsLabel(44, ttl=32),
+                                      VppMplsLabel(46, MplsLspMode.UNIFORM)])],
+                is_l2=1)
+            mpls_tun.add_vpp_config()
+            mpls_tun.admin_up()
 
     def test_v4_exp_null(self):
         """ MPLS V4 Explicit NULL test """