Some platforms (e.g. Amiga OS) do not have `PF_INET6`. Adjust the code
for these.
```
hostip.c: In function 'fetch_addr':
hostip.c:308:12: error: 'PF_INET6' undeclared (first use in this function)
pf = PF_INET6;
^~~~~~~~
```
Regression from
1902e8fc511078fb5e26fc2b907b4cce77e1240d
Reviewed-by: Daniel Stenberg
Closes #9760
bool found = false;
struct Curl_addrinfo *addr = dns->addr;
+#ifdef PF_INET6
if(data->conn->ip_version == CURL_IPRESOLVE_V6)
pf = PF_INET6;
+#endif
while(addr) {
if(addr->ai_family == pf) {