Perform forward DNS lookups to verify the correctness of the reverse DNS lookup

[ahf]

Currently the hostname is determent purely based on the result of the reverse DNS lookup. This is incorrect. The result of the reverse DNS lookup should be looked up using forward DNS too and verify if they match.

ip := client.ip
rdns := ReverseDNSLookup(ip)
fdns := ForwardDNSLookup(rdns)

if rdns == fdns then
    return rdns
else
    return ip