mgmtd: Prevent use after free

[donaldsharp]

ci is picking up this use after free on occasion:

ERROR: AddressSanitizer: attempting to call malloc_usable_size() for pointer which is not owned: 0x6030001d94a0
    0 0x7fab994b7f04 in __interceptor_malloc_usable_size ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:119
    1 0x7fab994264f6 in __sanitizer::BufferedStackTrace::Unwind(unsigned long, unsigned long, void*, bool, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_stacktrace.h:131
    2 0x7fab994264f6 in __asan::asan_malloc_usable_size(void const*, unsigned long, unsigned long) ../../../../src/libsanitizer/asan/asan_allocator.cpp:1058
    3 0x7fab99039bcf in mt_count_free lib/memory.c:78
    4 0x7fab99039bcf in qfree lib/memory.c:130
    5 0x7fab98ff971a in hash_clean lib/hash.c:290
    6 0x56110cdb0e7f in mgmt_txn_hash_destroy mgmtd/mgmt_txn.c:1881
    7 0x56110cdb0e7f in mgmt_txn_destroy mgmtd/mgmt_txn.c:2013
    8 0x56110cd8e5de in mgmt_terminate mgmtd/mgmt.c:91
    9 0x56110cd8e003 in sigint mgmtd/mgmt_main.c:90
    10 0x7fab990bf4b0 in frr_sigevent_process lib/sigevent.c:117
    11 0x7fab990ea7a1 in event_fetch lib/event.c:1740
    12 0x7fab9901a24e in frr_run lib/libfrr.c:1245
    13 0x56110cd8e21f in main mgmtd/mgmt_main.c:290
    14 0x7fab98af9249 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    15 0x7fab98af9304 in __libc_start_main_impl ../csu/libc-start.c:360
    16 0x56110cd8dd30 in _start (/usr/lib/frr/mgmtd+0x3ad30)

0x6030001d94a0 is located 0 bytes inside of 24-byte region [0x6030001d94a0,0x6030001d94b8)
freed by thread T0 here:
    0 0x7fab994b76a8 in __interceptor_free ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:52
    1 0x7fab99039bf0 in qfree lib/memory.c:131
    2 0x7fab98ff93e1 in hash_release lib/hash.c:227
    3 0x56110cdaabdc in mgmt_txn_unlock mgmtd/mgmt_txn.c:1931
    4 0x56110cdab049 in mgmt_txn_delete mgmtd/mgmt_txn.c:1841
    5 0x56110cdab0ce in mgmt_txn_hash_free mgmtd/mgmt_txn.c:1864
    6 0x7fab98ff970b in hash_clean lib/hash.c:288
    7 0x56110cdb0e7f in mgmt_txn_hash_destroy mgmtd/mgmt_txn.c:1881
    8 0x56110cdb0e7f in mgmt_txn_destroy mgmtd/mgmt_txn.c:2013
    9 0x56110cd8e5de in mgmt_terminate mgmtd/mgmt.c:91
    10 0x56110cd8e003 in sigint mgmtd/mgmt_main.c:90
    11 0x7fab990bf4b0 in frr_sigevent_process lib/sigevent.c:117
    12 0x7fab990ea7a1 in event_fetch lib/event.c:1740
    13 0x7fab9901a24e in frr_run lib/libfrr.c:1245
    14 0x56110cd8e21f in main mgmtd/mgmt_main.c:290
    15 0x7fab98af9249 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

previously allocated by thread T0 here:
    0 0x7fab994b83b7 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:77
    1 0x7fab990392fd in qcalloc lib/memory.c:106
    2 0x7fab98ff8b4f in hash_get lib/hash.c:156
    3 0x56110cdb13ae in mgmt_txn_create_new mgmtd/mgmt_txn.c:1825
    4 0x56110cdb3b4d in mgmt_txn_notify_be_adapter_conn mgmtd/mgmt_txn.c:2212
    5 0x56110cd91178 in mgmt_be_adapter_conn_init mgmtd/mgmt_be_adapter.c:842
    6 0x7fab990ec6de in event_call lib/event.c:2019
    7 0x7fab9901a243 in frr_run lib/libfrr.c:1246
    8 0x56110cd8e21f in main mgmtd/mgmt_main.c:290
    9 0x7fab98af9249 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

The only time that mgmt_txn_hash_free is called is in hash_clean. There are other places that mgmt_txn_unlock/delete are called and hash_release should be called. Let's just notice when mgmtd is being called from the hash_clean and not call hash_release (since we know it is being released already)