nhrpd: Fix nhrp_peer leak (backport #14579)

[mergify]

• Addressed memory leak by removing &c->peer_notifier from the notifier list on termination. Retaining it caused the notifier list to stay active, preventing the deletion of c->cur.peer thereby causing a memory leak.

• Reordered termination steps to call vrf_terminate before nhrp_vc_terminate, preventing a heap-use-after-free issue when nhrp_vc_notify_del is invoked in nhrp_peer_check_delete.

• Added an if statement to avoid passing NULL as hash to hash_release, which leads to a SIGSEGV.

The ASan leak log for reference:

***********************************************************************************
Address Sanitizer Error detected in nhrp_topo.test_nhrp_topo/r1.asan.nhrpd.20265

=================================================================
==20265==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 112 byte(s) in 1 object(s) allocated from:
    #0 0x7f80270c9b40 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdeb40)
    #1 0x7f8026ac1eb8 in qmalloc lib/memory.c:100
    #2 0x560fd648f0a6 in nhrp_peer_create nhrpd/nhrp_peer.c:175
    #3 0x7f8026a88d3f in hash_get lib/hash.c:147
    #4 0x560fd6490a5d in nhrp_peer_get nhrpd/nhrp_peer.c:228
    #5 0x560fd648a51a in nhrp_nhs_resolve_cb nhrpd/nhrp_nhs.c:297
    #6 0x7f80266b000f in resolver_cb_literal lib/resolver.c:234
    #7 0x7f8026b62e0e in event_call lib/event.c:1969
    #8 0x7f8026aa5437 in frr_run lib/libfrr.c:1213
    #9 0x560fd6488b4f in main nhrpd/nhrp_main.c:166
    #10 0x7f8025eb2c86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21c86)

SUMMARY: AddressSanitizer: 112 byte(s) leaked in 1 allocation(s).
***********************************************************************************

***********************************************************************************
Address Sanitizer Error detected in nhrp_topo.test_nhrp_topo/r2.asan.nhrpd.20400

=================================================================
==20400==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 112 byte(s) in 1 object(s) allocated from:
    #0 0x7fb6e3ca5b40 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdeb40)
    #1 0x7fb6e369deb8 in qmalloc lib/memory.c:100
    #2 0x562652de40a6 in nhrp_peer_create nhrpd/nhrp_peer.c:175
    #3 0x7fb6e3664d3f in hash_get lib/hash.c:147
    #4 0x562652de5a5d in nhrp_peer_get nhrpd/nhrp_peer.c:228
    #5 0x562652de1e8e in nhrp_packet_recvraw nhrpd/nhrp_packet.c:325
    #6 0x7fb6e373ee0e in event_call lib/event.c:1969
    #7 0x7fb6e3681437 in frr_run lib/libfrr.c:1213
    #8 0x562652dddb4f in main nhrpd/nhrp_main.c:166
    #9 0x7fb6e2a8ec86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21c86)

SUMMARY: AddressSanitizer: 112 byte(s) leaked in 1 allocation(s).
***********************************************************************************
```<hr>This is an automatic backport of pull request #14579 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of d163f89 has failed:

On branch mergify/bp/stable/9.1/pr-14579
Your branch is up to date with 'origin/stable/9.1'.

You are currently cherry-picking commit d163f89e1.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   nhrpd/nhrp_cache.c
	modified:   nhrpd/nhrp_peer.c

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   nhrpd/nhrp_main.c

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[ton31337]

Manual backport #16166, closing this.