Set pass_last_set_time when password is set

pass_last_set_time field should be kept up to date or Samba may assume that password is invalid (in such case, pass_must_change_time is treated as 0 regardless a field in the same name).

source3/passdb/pdb_get_set.c

```C
time_t pdb_get_pass_must_change_time(const struct samu *sampass)
{
        uint32_t expire;

        if (sampass->pass_last_set_time == 0)
                return (time_t) 0;

        if (sampass->acct_ctrl & ACB_PWNOEXP)
                return pdb_password_change_time_max();

        if (!pdb_get_account_policy(PDB_POLICY_MAX_PASSWORD_AGE, &expire)
            || expire == (uint32_t)-1 || expire == 0)
                return get_time_t_max();

        return sampass->pass_last_set_time + expire;
}
```