[teamsyncd]: Do not update lag mtu from teamsyncd (netlink)

[prsunny]

What I did
Revert changes done as part of #922

Why I did it
In some use-cases it is required that kernel MTU is different (may be default 1500) from the config_db value (say 9000). In this case, if teamsyncd updates the MTU value via Netlink, orchagent/asic mtu value would be different from the user configured value. We want teammgr which listens on config db to update the mtu value to APP_DB.

Original change was done due to a timing issue where mtu value was found to be missing in APP_DB. This resulted in orchagent creating router interface with 1492 mtu value - Logs are in details

How I verified it
Load the changes and reboot, config reload and check if mtu is correct in APP_DB as expected.

Details if related

Jun  4 01:39:58.250123 str-7260cx3-acs-1 NOTICE teamd#teammgrd: :- setLagAdminStatus: Set port channel PortChannel0001 admin status to up
Jun  4 01:39:58.260106 str-7260cx3-acs-1 NOTICE teamd#teammgrd: :- setLagMtu: Set port channel PortChannel0001 MTU to 9100
Jun  4 01:39:59.479761 str-7260cx3-acs-1 INFO teamd#teamsyncd: :- addLag: Add PortChannel0001 admin_status:up oper_status:down, mtu: 9100
Jun  4 01:40:10.860972 str-7260cx3-acs-1 NOTICE teamd#teammgrd: :- addLagMember: Add Ethernet52 to port channel PortChannel0001
Jun  4 01:40:10.889090 str-7260cx3-acs-1 INFO teamd#teamsyncd: :- addLag: Add PortChannel0001 admin_status:up oper_status:down, mtu: 9100
Jun  4 01:40:10.889173 str-7260cx3-acs-1 INFO teamd#teamsyncd: :- addLag: Add PortChannel0001 admin_status:up oper_status:up, mtu: 9100
Jun  4 01:40:10.928183 str-7260cx3-acs-1 INFO teamd#teamsyncd: :- addLag: Add PortChannel0001 admin_status:up oper_status:up, mtu: 9100
Jun  4 01:40:10.939448 str-7260cx3-acs-1 NOTICE teamd#teammgrd: :- addLagMember: Add Ethernet48 to port channel PortChannel0001
Jun  4 01:40:10.990113 str-7260cx3-acs-1 INFO teamd#teamsyncd: :- addLag: Add PortChannel0001 admin_status:up oper_status:up, mtu: 9100
Jun  4 01:40:27.189900 str-7260cx3-acs-1 NOTICE swss#orchagent: :- doLagTask: Create port: LAG PortChannel0001 mtu 0
Jun  4 01:40:27.190029 str-7260cx3-acs-1 NOTICE swss#orchagent: :- addLag: Create an empty LAG PortChannel0001 lid:200000013fff2
Jun  4 01:40:27.190489 str-7260cx3-acs-1 NOTICE swss#orchagent: :- doLagTask: --> MTU: LAG PortChannel0001 mtu 0
Jun  4 01:40:27.264062 str-7260cx3-acs-1 NOTICE swss#orchagent: :- addRouterIntfs: Create router interface PortChannel0001 MTU 1492

[prsunny]

@hzheng5, please review