- What I did

Previously, if a port mapping specified a host IP or port that could not be used because the endpoint's network was in routed mode (so, there's no host binding), it'd be treated as an error.

However:

• the selected gateway endpoint may change over time, as networks are connected and disconnected - so the binding may make sense for some other endpoint.
• the validation was complicated, duplicated logic in order to fail early, and wasn't complete.

- How I did it

So, just log when fields are ignored, at the point where they're ignored.

Removed the old validation function and its test.

Give the port mapping code a context containing a logger that adds network and endpoint ids.

- How to verify it

Added unit tests for cases that were previously errors, checking the log output.

Example of the log message with extra context:

# DOCKER_USERLANDPROXY=false hack/make.sh run

# docker network create b4
# docker run --rm -ti --network b4 -p [::1]:8080:80 nginx

INFO[2024-10-03T14:15:19.298614757Z] Cannot map from IPv6 to an IPv4-only container because the userland proxy is disabled  eid=a8005de0bc9e294b83ae31aefdd17bb65e8055f75fd6a88eafe411557411228b mapping="[::1]:8080:80/tcp" nid=cbbe0a39ecb8522b791e0c44ae106820f3eea6f5404e5656557e9f138108bfc9 spanID=02e5a360305a8237 traceID=d2de070d083025c8a0bbdc7d7c6fe9aa

- Description for the changelog

Log rather than error if a port mapping includes a host IP address or port number that
cannot be used because NAT from the host is disabled. The unused fields may be needed
if the gateway endpoint changes when networks are connected or disconnected.