Timeouts for IPv4 ACD should be configurable

[bengal]

Component

systemd-networkd

Is your feature request related to a problem? Please describe

When using the timeouts specified by RFC 5227 for Address Conflict Detection, a complete probe can take up to 9 seconds. In this interval, IPv4 addresses will not be present on the interface, delaying any service that need them. Section 2.2 of the RFC says:

 Network technologies may emerge for which shorter delays are
 appropriate than those required by this document.  A subsequent IETF
 publication may be produced providing guidelines for different values
 for PROBE_WAIT, PROBE_NUM, PROBE_MIN, and PROBE_MAX on those
 technologies.

On modern networking technologies the round-trip latency is typically few milliseconds and so the values from the RFC are totally inadequate. A total timeout of e.g. 200ms or even less would be fine in most cases and would provide a better user experience.

Describe the solution you'd like

The timeouts should be configurable. There should be a new option (i.e. DuplicateAddressDetectionMaxTimeout ) that specifies the maximux timeout, and the various sub-intervals should be scaled accordingly. The n-acd library does something similar: https://github.com/nettools/n-acd/blob/master/src/n-acd-probe.c#L57

Optionally, the default value of the timeout should be changed to a shorter value.

Describe alternatives you've considered

No response

The systemd version you checked that didn't have the feature you are asking for

No response