all: implement RFC8910 §3 URI equality check

all: implement RFC8910 §3 URI equality check

§3 Precedence of API URIs
"
A device may learn about Captive Portal API URIs through more than one of (or
indeed all of) the above options. Implementations can select their own
precedence order (e.g., prefer one of the IPv6 options before the DHCPv4 option,
or vice versa, et cetera).

If the URIs learned via more than one option described in Section 2 are not all
identical, this condition should be logged for the device owner or
administrator; it is a network configuration error if the learned URIs are not
all identical.
"

We log the 'network configuration error' but proceed in an attempt to be useful
(since the RFC makes no mention of disregarding the URI) and prefer DHCPv6,
since this is the DHCPv6 client.

Signed-off-by: Paul Donald <[email protected]>
Link: https://github.com/openwrt/odhcp6c/pull/127
Signed-off-by: Álvaro Fernández Rojas <[email protected]>