selftests: forwarding: Fix race condition in mirror installation

When mirroring to a gretap in hardware the device expects to be
programmed with the egress port and all the encapsulating headers. This
requires the driver to resolve the path the packet will take in the
software data path and program the device accordingly.

If the path cannot be resolved (in this case because of an unresolved
neighbor), then mirror installation fails until the path is resolved.
This results in a race that causes the test to sometimes fail.

Fix this by setting the neighbor's state to permanent in a couple of
tests, so that it is always valid.

Fixes: 35c31d5c ("selftests: forwarding: Test mirror-to-gretap w/ UL 802.1d")
Fixes: 239e754a ("selftests: forwarding: Test mirror-to-gretap w/ UL 802.1q")
Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Link: https://lore.kernel.org/r/268816ac729cb6028c7a34d4dda6f4ec7af55333.1687264607.git.petrm@nvidia.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

tools/testing/selftests/net/forwarding/mirror_gre_bridge_1d.sh

@@ -93,12 +93,16 @@ cleanup()
 
 test_gretap()
 {
+	ip neigh replace 192.0.2.130 lladdr $(mac_get $h3) \
+		 nud permanent dev br2
 	full_test_span_gre_dir gt4 ingress 8 0 "mirror to gretap"
 	full_test_span_gre_dir gt4 egress 0 8 "mirror to gretap"
 }
 
 test_ip6gretap()
 {
+	ip neigh replace 2001:db8:2::2 lladdr $(mac_get $h3) \
+		nud permanent dev br2
 	full_test_span_gre_dir gt6 ingress 8 0 "mirror to ip6gretap"
 	full_test_span_gre_dir gt6 egress 0 8 "mirror to ip6gretap"
 }

tools/testing/selftests/net/forwarding/mirror_gre_bridge_1q.sh

@@ -90,12 +90,16 @@ cleanup()
 
 test_gretap()
 {
+	ip neigh replace 192.0.2.130 lladdr $(mac_get $h3) \
+		 nud permanent dev br1
 	full_test_span_gre_dir gt4 ingress 8 0 "mirror to gretap"
 	full_test_span_gre_dir gt4 egress 0 8 "mirror to gretap"
 }
 
 test_ip6gretap()
 {
+	ip neigh replace 2001:db8:2::2 lladdr $(mac_get $h3) \
+		nud permanent dev br1
 	full_test_span_gre_dir gt6 ingress 8 0 "mirror to ip6gretap"
 	full_test_span_gre_dir gt6 egress 0 8 "mirror to ip6gretap"
 }