[arista]: Always set sai_tunnel_support on Arista-7260cx3 (#16097)

Why I did it
To overwrite the default DSCP_TO_TC_MAP for tunnel traffic, the attribute sai_tunnel_support must be set to 1.
Before this change, the attribute is set only on dual-tor platform when remap is enabled.
This PR is to set the attribute on all Arista-7260cx3 devices.

Work item tracking
Microsoft ADO 24785776

How I did it
Update the config.bcm template for Arista-7260cx3 devices.

How to verify it
The change is verified by manually rendering the j2 on a T1 testbed.

device/arista/x86_64-arista_7260cx3_64/Arista-7260CX3-C64/config.bcm.j2

@@ -14,8 +14,7 @@
 {%-         set switch_subtype = DEVICE_METADATA['localhost']['subtype'] -%}
 {%-         if 'dualtor' in switch_subtype.lower() %}
 {%-             set IPinIP_sock =
-'sai_tunnel_support=1
-sai_tunnel_underlay_route_mode=1
+'sai_tunnel_underlay_route_mode=1
 host_as_route_disable=1
 l3_ecmp_levels=2' -%}
 {%-             set map_prio = 'sai_remap_prio_on_tnl_egress=1' -%}
@@ -1049,5 +1048,6 @@ serdes_preemphasis_116=0x103706
 serdes_preemphasis_117=0x133c06
 
 {{ mmu_sock }}
+sai_tunnel_support=1
 {{ IPinIP_sock }}
 phy_an_lt_msft=1

device/arista/x86_64-arista_7260cx3_64/Arista-7260CX3-D108C10/config.bcm.j2

@@ -6,8 +6,7 @@
 {%-     set switch_subtype = DEVICE_METADATA['localhost']['subtype'] -%}
 {%-     if 'dualtor' in switch_subtype.lower() %}
 {%-         set IPinIP_sock =
-'sai_tunnel_support=1
-sai_tunnel_underlay_route_mode=1
+'sai_tunnel_underlay_route_mode=1
 host_as_route_disable=1
 l3_ecmp_levels=2' -%}
 {%-         set map_prio = 'sai_remap_prio_on_tnl_egress=1' -%}
@@ -956,5 +955,6 @@ serdes_preemphasis_130=0x580c
 serdes_preemphasis_131=0x580c
 
 mmu_init_config="MSFT-TH2-Tier0"
+sai_tunnel_support=1
 {{ IPinIP_sock }}
 phy_an_lt_msft=1

device/arista/x86_64-arista_7260cx3_64/Arista-7260CX3-D108C8/config.bcm.j2

@@ -6,8 +6,7 @@
 {%-     set switch_subtype = DEVICE_METADATA['localhost']['subtype'] -%}
 {%-     if 'dualtor' in switch_subtype.lower() %}
 {%-         set IPinIP_sock =
-'sai_tunnel_support=1
-sai_tunnel_underlay_route_mode=1
+'sai_tunnel_underlay_route_mode=1
 host_as_route_disable=1
 l3_ecmp_levels=2' -%}
 {%-         set map_prio = 'sai_remap_prio_on_tnl_egress=1' -%}
@@ -960,5 +959,6 @@ serdes_preemphasis_130=0x580c
 serdes_preemphasis_131=0x580c
 
 mmu_init_config="MSFT-TH2-Tier0"
+sai_tunnel_support=1
 {{ IPinIP_sock }}
 phy_an_lt_msft=1

device/arista/x86_64-arista_7260cx3_64/Arista-7260CX3-Q64/config.bcm.j2

@@ -14,8 +14,7 @@
 {%-         set switch_subtype = DEVICE_METADATA['localhost']['subtype'] -%}
 {%-         if 'dualtor' in switch_subtype.lower() %}
 {%-             set IPinIP_sock =
-'sai_tunnel_support=1
-sai_tunnel_underlay_route_mode=1
+'sai_tunnel_underlay_route_mode=1
 host_as_route_disable=1
 l3_ecmp_levels=2' -%}
 {%-             set map_prio = 'sai_remap_prio_on_tnl_egress=1' -%}
@@ -1048,5 +1047,6 @@ serdes_preemphasis_116=0x105004
 serdes_preemphasis_117=0x105004
 
 {{ mmu_sock }}
+sai_tunnel_support=1
 {{ IPinIP_sock }}
 phy_an_lt_msft=1

src/sonic-config-engine/tests/data/j2_template/config.bcm.j2

@@ -14,8 +14,7 @@
 {%-         set switch_subtype = DEVICE_METADATA['localhost']['subtype'] -%}
 {%-         if 'dualtor' in switch_subtype.lower() %}
 {%-             set IPinIP_sock =
-'sai_tunnel_support=1
-sai_tunnel_underlay_route_mode=1
+'sai_tunnel_underlay_route_mode=1
 host_as_route_disable=1
 l3_ecmp_levels=2' -%}
 {%-             set map_prio = 'sai_remap_prio_on_tnl_egress=1' -%}
@@ -33,5 +32,6 @@ sai_pfc_dlr_init_capability=1' -%}
 l3_alpm_hit_skip=1
 {{ map_prio }}
 {{ mmu_sock }}
+sai_tunnel_support=1
 {{ IPinIP_sock }}
 {{ pfcwd_sock }}

src/sonic-config-engine/tests/sample_output/py3/arista7260-t1.config.bcm

@@ -2,6 +2,7 @@
 l3_alpm_hit_skip=1
 
 mmu_init_config="MSFT-TH2-Tier1"
+sai_tunnel_support=1
 
 hybrid_pfc_deadlock_enable=1
 pfc_deadlock_seq_control=1