[device config] Adding configuration for default route fallback (#10465)

* [device config] Adding configuration for default route fallback
* Set sai_tunnel_underlay_route_mode attribute to fallback to default route if more specific route is unavailable.

Author: Ndancejic

device/arista/x86_64-arista_7050cx3_32s/Arista-7050CX3-32S-C32/td3-a7050cx3-32s-32x100G.config.bcm

@@ -5,6 +5,7 @@ host_as_route_disable=1
 use_all_splithorizon_groups=1
 riot_enable=1
 sai_tunnel_support=1
+sai_tunnel_underlay_route_mode=1
 riot_overlay_l3_intf_mem_size=4096
 riot_overlay_l3_egress_mem_size=32768
 l3_ecmp_levels=2

device/arista/x86_64-arista_7050cx3_32s/Arista-7050CX3-32S-D48C8/td3-a7050cx3-32s-48x50G+8x100G.config.bcm

@@ -5,6 +5,7 @@ host_as_route_disable=1
 use_all_splithorizon_groups=1
 riot_enable=1
 sai_tunnel_support=1
+sai_tunnel_underlay_route_mode=1
 riot_overlay_l3_intf_mem_size=4096
 riot_overlay_l3_egress_mem_size=32768
 l3_ecmp_levels=2

device/arista/x86_64-arista_7050cx3_32s/td3-a7050cx3-32s-flex.config.bcm

@@ -397,6 +397,7 @@ robust_hash_disable_mpls=1
 robust_hash_disable_vlan=1
 sai_load_hw_config=/etc/bcm/flex/bcm56870_a0_premium_issu/b870.6.4.1/
 sai_tunnel_support=1
+sai_tunnel_underlay_route_mode=1
 serdes_core_rx_polarity_flip_physical{1}=0x8
 serdes_core_rx_polarity_flip_physical{5}=0x2
 serdes_core_rx_polarity_flip_physical{9}=0xc

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

@@ -12,6 +12,7 @@
 {%-         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
                                    host_as_route_disable=1
                                    l3_ecmp_levels=2' -%}
 {%-         endif %}

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

@@ -4,6 +4,7 @@
 {%-     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
                                host_as_route_disable=1
                                l3_ecmp_levels=2' -%}
 {%-     endif %}

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

@@ -12,6 +12,7 @@
 {%-         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
                                    host_as_route_disable=1
                                    l3_ecmp_levels=2' -%}
 {%-         endif %}

src/sonic-device-data/tests/permitted_list

@@ -2,6 +2,7 @@ sai_trap_group_priority
 use_all_splithorizon_groups
 riot_enable
 sai_tunnel_support
+sai_tunnel_underlay_route_mode
 riot_overlay_l3_intf_mem_size
 riot_overlay_l3_egress_mem_size
 l3_ecmp_levels