Traffic disruption during warm-boot due to invalid LAG MTU configuration

[nazariig]

sonic_dump_arc-switch1025_20200910_164801.tar.gz

The current apply_temp_view logic doesn't handle MTU configuration during warm-reboot:

Before warm-reboot:

root@sonic:/home/admin# redis-cli -n 0 HGETALL 'LAG_TABLE:PortChannel0001'
1) "admin_status"
2) "up"
3) "oper_status"
4) "up"
5) "mtu"
6) "9100"

After warm-reboot:

root@sonic:/home/admin# redis-cli -n 0 HGETALL 'LAG_TABLE:PortChannel0001'
1) "admin_status"
2) "up"
3) "oper_status"
4) "up"

Apply state logs:

Aug 31 09:46:37.787959 sonic NOTICE teamd#teamsyncd: :- applyState: Applying state
Aug 31 09:46:37.789065 sonic NOTICE teamd#teamsyncd: :- dump: getting took 0.000322 sec
Aug 31 09:46:37.789065 sonic INFO teamd#teamsyncd: :- apply_temp_view: View switch of table LAG_TABLE required.
Aug 31 09:46:37.789065 sonic INFO teamd#teamsyncd: :- apply_temp_view: Objects in current view:
Aug 31 09:46:37.789065 sonic INFO teamd#teamsyncd: :- apply_temp_view:     PortChannel0001: 3 fields;
Aug 31 09:46:37.789065 sonic INFO teamd#teamsyncd: :- apply_temp_view: Objects in target view:
Aug 31 09:46:37.789065 sonic INFO teamd#teamsyncd: :- apply_temp_view:     PortChannel0001: 2 fields;
Aug 31 09:46:37.790676 sonic NOTICE teamd#teamsyncd: :- dump: getting took 0.000214 sec
Aug 31 09:46:37.790676 sonic INFO teamd#teamsyncd: :- apply_temp_view: View switch of table LAG_MEMBER_TABLE required.
Aug 31 09:46:37.790676 sonic INFO teamd#teamsyncd: :- apply_temp_view: Objects in current view:
Aug 31 09:46:37.790676 sonic INFO teamd#teamsyncd: :- apply_temp_view:     PortChannel0001:Ethernet16: 1 fields;
Aug 31 09:46:37.790676 sonic INFO teamd#teamsyncd: :- apply_temp_view: Objects in target view:
Aug 31 09:46:37.790722 sonic INFO teamd#teamsyncd: :- apply_temp_view:     PortChannel0001:Ethernet16: 1 fields;
Aug 31 09:46:37.791751 sonic NOTICE teamd#teamsyncd: :- setWarmStartState: teamsyncd warm start state changed to reconciled

This ends up in traffic disruption after ISSU end:

Aug 31 07:57:07.043050 sonic NOTICE swss#orchagent: :- addRouterIntfs: Create router interface Ethernet116 MTU 9100
Aug 31 07:57:07.052926 sonic NOTICE swss#orchagent: :- addRouterIntfs: Create router interface PortChannel0001 MTU 1492
Aug 31 07:57:07.204451 sonic NOTICE swss#orchagent: :- addRouterIntfs: Create router interface Vlan23 MTU 9100

Aug 31 07:57:07.554444 sonic INFO syncd#supervisord: syncd Aug 31 07:57:07 NOTICE  SAI_RIF: mlnx_sai_rif.c[566]- mlnx_create_router_interface: Create rif, #0 VIRTUAL_ROUTER_ID=VIRTUAL_ROUTER,(0:0),0,0000,0 #1 SRC_MAC_ADDRESS=[50:6b:4b:96:5e:00] #2 TYPE=PORT #3 PORT_ID=PORT,(0:0),11b00,0000,0 #4 MTU=9100
Aug 31 07:57:07.573953 sonic INFO syncd#supervisord: syncd Aug 31 07:57:07 NOTICE  SAI_RIF: mlnx_sai_rif.c[566]- mlnx_create_router_interface: Create rif, #0 VIRTUAL_ROUTER_ID=VIRTUAL_ROUTER,(0:0),0,0000,0 #1 SRC_MAC_ADDRESS=[50:6b:4b:96:5e:00] #2 TYPE=PORT #3 PORT_ID=LAG,(0:0),40,0000,0 #4 MTU=1492
Aug 31 07:57:07.599988 sonic INFO syncd#supervisord: syncd Aug 31 07:57:07 NOTICE  SAI_RIF: mlnx_sai_rif.c[566]- mlnx_create_router_interface: Create rif, #0 VIRTUAL_ROUTER_ID=VIRTUAL_ROUTER,(0:0),0,0000,0 #1 SRC_MAC_ADDRESS=[50:6b:4b:96:5e:00] #2 TYPE=VLAN #3 VLAN_ID=VLAN,(0:0),17,0000,0 #4 MTU=9100

Aug 31 07:57:11.967761 sonic INFO syncd#supervisord: syncd Aug 31 07:57:11 NOTICE  SAI_UTILS: mlnx_sai_utils.c[2397]- set_dispatch_attrib_handler: Set FAST_API_ENABLE, key:Switch ID 1, val:false

Aug 31 07:57:22.013521 sonic NOTICE swss#orchagent: :- setRouterIntfsMtu: Set router interface Vlan23 MTU to 9100
Aug 31 07:57:22.016550 sonic INFO syncd#supervisord: syncd Aug 31 07:57:22 NOTICE  SAI_UTILS: mlnx_sai_utils.c[2397]- set_dispatch_attrib_handler: Set MTU, key:rif idx 3, val:9100
Aug 31 07:57:22.017188 sonic NOTICE swss#orchagent: :- setRouterIntfsMtu: Set router interface PortChannel0001 MTU to 9100
Aug 31 07:57:22.021689 sonic INFO syncd#supervisord: syncd Aug 31 07:57:22 NOTICE  SAI_UTILS: mlnx_sai_utils.c[2397]- set_dispatch_attrib_handler: Set MTU, key:rif idx 2, val:9100

Fix #1423