[intfmgrd] Flush IPv4 link local neighbors while removing router intf

[gord1306]

What I did [intfmgrd] Flush IPv4 link local neighbors while removing router intf

Why I did it When removing the router interface, ensure to also flush the IPv4 Link-Local neighbors. If there is no IP address on the router interface, the IPv4 Link-Local neighbors may not automatically disappear. This can prevent the failure removal of the router interface due to it being referenced by the neighbor entries.

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