Failure in compilation of sim_hostusrsock.c due to improper handling of header inclusion for fd_set

Compilation failure may result due to missing header which defines the fd_set structure in [sim_hostusrsock.c](https://github.com/apache/nuttx/blob/master/arch/sim/src/sim/posix/sim_hostusrsock.c#L49-L50).

```
/home/ritvik/Desktop/Files/Fuzzing_RTOS_Applications/Ported_Applications/nuttxspace/nuttx/arch/sim/src/sim/posix/sim_hostusrsock.c:51:8: error: unknown type name 'fd_set'
51 | static fd_set g_active_read_fds;
| ^
/home/ritvik/Desktop/Files/Fuzzing_RTOS_Applications/Ported_Applications/nuttxspace/nuttx/arch/sim/src/sim/posix/sim_hostusrsock.c:52:8: error: unknown type name 'fd_set'
52 | static fd_set g_active_write_fds;
```

fd_set is only defined in [select.h](https://github.com/apache/nuttx/blob/c655870b22736e53982efdd4f8c8f8c919ed8320/include/sys/select.h#L106) which should be included in this header or any of the subsequent headers included in this file.