[sr-dev] [kamailio/kamailio] the recursive lock of tm module is not safe? (Issue #3083)

### Description See `lock_hash` in `h_table.c`:

```C void lock_hash(int i) { int mypid;

mypid = my_pid(); if (likely(atomic_get(&_tm_table->entries[i].locker_pid) != mypid)) { lock(&_tm_table->entries[i].mutex); atomic_set(&_tm_table->entries[i].locker_pid, mypid); } else { /* locked within the same process that called us*/ _tm_table->entries[i].rec_lock_level++; } } ```

Flowing lines of code do not guarantee atomicity and I think it is not safe: * atomic_get(&_tm_table->entries[i].locker_pid) != mypid * lock(&_tm_table->entries[i].mutex) * atomic_set(&_tm_table->entries[i].locker_pid, mypid)

Would you mind solving my confusion?