ospfd: Fix several problems with direct and delayed acknowledgments (backport #16351)

[mergify]

1. On P2MP interfaces, direct ack would include the same LSA multiple times multiple packets are processed before the OSPF interfae direct LSA acknowledgment event is processed. Now duplicates LSA in the same event are suppressed.
2. On non-broadcast interfaces, direct acks for multiple neighbors would be unicast to the same neighbor due to the multiple OSPF LS Update packets being process prior to the OSPF interface direct ack event. Now, separate direct acks are unicast to the neighbors requiring them.
3. The interface delayed acknowledgment timer runs would run continously (every second as long as the interace is up). Now, the timer is set when delayed acknowledgments are queued and all queued delayed acknowledges are sent when it fires.
4. For non-broadcast interface delayed acknowledgments, the logic to send to multiple neighbors wasn't working because the list was emptied while building the packet for the first neighbor.

   ---

   This is an automatic backport of pull request ospfd: Fix several problems with direct and delayed acknowledgments  #16351 done by Mergify.

[mergify]

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Changes to be committed:
	modified:   lib/libospf.h
	modified:   ospfd/ospf_flood.c
	modified:   ospfd/ospf_interface.c
	modified:   ospfd/ospf_interface.h
	modified:   ospfd/ospf_ism.c

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   ospfd/ospf_flood.h
	both modified:   ospfd/ospf_packet.c
	both modified:   ospfd/ospf_packet.h

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