[ZTP] Add vendor specific hook to check link state

[lotus-nexthop]

What I did
Use get_management_port_link_status_override from sonic platform API introduced by sonic-net/sonic-platform-common#654 to determine management port link status for ZTP.

Why I did it

Nexthop's platforms have an unmanaged switch sitting between the front panel rj45 and the CPU's eth0.
As a result eth0's link state as advertised by the kernel (/sys/class/net/eth0/operstate), does not reflect the state of the rj45.

e.g.

Front Panel RJ45 (Management Port)
         |
        A
         |
    BCM53134 Switch (management switch running in unmanaged mode)
       /    \
      B      C
     /        \
    BMC    CPU (eth0)

Link A may be down (if RJ45 for example is unplugged), but link C (/sys/class/net/eth0/operstate) still says up.

in this PR we avoid needlessly attempting to access eth0 (eth0 is just an example, can be any management port) in ZTP if eth0 is down on platforms where /sys/class/net/eth0/operstate link being up is not enough information to indicate management port being up.

[mssonicbld]

/azp run

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[mssonicbld]

/azp run

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