skip vxlan_decap testcase on cisco 8122 platform (#15219)

tests/common/plugins/conditional_mark/tests_mark_conditions.yaml

@@ -1943,6 +1943,12 @@ vxlan/test_vxlan_crm.py::Test_VxLAN_Crm::test_crm_512_nexthop_groups[v6_in_v6]:
       - "asic_gen == 'spc1'"
       - "(is_multi_asic == True) or (platform not in ['x86_64-8102_64h_o-r0', 'x86_64-8101_32fh_o-r0', 'x86_64-mlnx_msn4600c-r0', 'x86_64-mlnx_msn2700-r0', 'x86_64-mlnx_msn2700a1-r0'])"
 
+vxlan/test_vxlan_decap.py:
+  skip:
+    reason: "vxlan support not available for cisco-8122 platforms"
+    conditions:
+      - "platform in ['x86_64-8122_64eh_o-r0', 'x86_64-8122_64ehf_o-r0']"
+
 vxlan/test_vxlan_ecmp.py:
   skip:
     reason: "VxLAN ECMP test is not yet supported on multi-ASIC platform. Also this test can only run on 4600c, 2700 and 8102."