DNSSEC: fix clang warning re && in || precedence

I looked and AFAICT the compiler guidance gives the correct logical
binding for the code intention.

```
dnsdb.c:362:32: warning: '&&' within '||' [-Wlogical-op-parentheses]
       || dnssec_mode == DEFER && !dns_is_secure(&dnsa)
       ~~ ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
dnsdb.c:362:32: note: place parentheses around the '&&' expression to silence this warning
       || dnssec_mode == DEFER && !dns_is_secure(&dnsa)
                               ^
          (                                            )
```