Take client IP address from EDNS if available

[ranile]

On OpenWRT, when dnscrypt-proxy is behind dnsmasq then the client IP is not directly available. It is possible to send the IP address of requester from dnsmasq using EDNS:

--add-subnet[[=[<IPv4 address>/]<IPv4 prefix length>][,[<IPv6 address>/]<IPv6 prefix length>]]
Add a subnet address to the DNS queries which are forwarded upstream. If an address is specified in the flag, it will be used, otherwise, the address of the requestor will be used. The amount of the address forwarded depends on the prefix length parameter: 32 (128 for IPv6) forwards the whole address, zero forwards none of it but still marks the request so that no upstream nameserver will add client address information either. The default is zero for both IPv4 and IPv6. Note that upstream nameservers may be configured to return different results based on this information, but the dnsmasq cache does not take account. Caching is therefore disabled for such replies, unless the subnet address being added is constant.

For example, --add-subnet=24,96 will add the /24 and /96 subnets of the requestor for IPv4 and IPv6 requestors, respectively. --add-subnet=1.2.3.4/24 will add 1.2.3.0/24 for IPv4 requestors and ::/0 for IPv6 requestors. --add-subnet=1.2.3.4/24,1.2.3.4/24 will add 1.2.3.0/24 for both IPv4 and IPv6 requestors.

From dnsmasq man page

dnscrypt-proxy should take the information from dnsmasq running with --add-subnet=32,128 and use it in logs and monitoring UI