selftests: net: local_termination: annotate the expected failures

Vladimir said when adding this test:

  The bridge driver fares particularly badly [...] mainly because
  it does not implement IFF_UNICAST_FLT.

See commit 90b9566a ("selftests: forwarding: add a test for
local_termination.sh").

We don't want to hide the known gaps, but having a test which
always fails prevents us from catching regressions. Report
the cases we know may fail as XFAIL.
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Link: https://lore.kernel.org/r/20240516152513.1115270-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -155,6 +155,7 @@ run_test()
 		"$smac > $MACVLAN_ADDR, ethertype IPv4 (0x0800)" \
 		true
 
+	xfail_on_veth $h1 \
 		check_rcv $rcv_if_name "Unicast IPv4 to unknown MAC address" \
 			"$smac > $UNKNOWN_UC_ADDR1, ethertype IPv4 (0x0800)" \
 			false
@@ -163,7 +164,9 @@ run_test()
 		"$smac > $UNKNOWN_UC_ADDR2, ethertype IPv4 (0x0800)" \
 		true
 
-	check_rcv $rcv_if_name "Unicast IPv4 to unknown MAC address, allmulti" \
+	xfail_on_veth $h1 \
+		check_rcv $rcv_if_name \
+			"Unicast IPv4 to unknown MAC address, allmulti" \
 			"$smac > $UNKNOWN_UC_ADDR3, ethertype IPv4 (0x0800)" \
 			false
 
@@ -171,7 +174,9 @@ run_test()
 		"$smac > $JOINED_MACV4_MC_ADDR, ethertype IPv4 (0x0800)" \
 		true
 
-	check_rcv $rcv_if_name "Multicast IPv4 to unknown group" \
+	xfail_on_veth $h1 \
+		check_rcv $rcv_if_name \
+			"Multicast IPv4 to unknown group" \
 			"$smac > $UNKNOWN_MACV4_MC_ADDR1, ethertype IPv4 (0x0800)" \
 			false
 
@@ -187,6 +192,7 @@ run_test()
 		"$smac > $JOINED_MACV6_MC_ADDR, ethertype IPv6 (0x86dd)" \
 		true
 
+	xfail_on_veth $h1 \
 		check_rcv $rcv_if_name "Multicast IPv6 to unknown group" \
 			"$smac > $UNKNOWN_MACV6_MC_ADDR1, ethertype IPv6 (0x86dd)" \
 			false