tools: Catch double pointer of struct thread towards thread_add_*

tools: Catch double pointer of struct thread towards thread_add_*

```
% spatch --sp-file tools/coccinelle/struct_thread_double_pointer.cocci --macro-file tools/cocci.h ./ 2>/dev/null
./lib/northbound_confd.c:429:65-66: Passed double 'struct thread' pointer
./lib/northbound_confd.c:1174:61-62: Passed double 'struct thread' pointer
./lib/northbound_sysrepo.c:543:69-70: Passed double 'struct thread' pointer
```

Signed-off-by: Donatas Abraitis <donatas.abraitis@gmail.com>