API: Log when too many values are passed for a multi-valued parameter

API: Log when too many values are passed for a multi-valued parameter

Currently the API just throws away the excess values, no continuation.
This is probably not the best behavior. There is a warning, but clients
are notorious for just ignoring warnings.

We could improve the situation:
* Turn it into an error.
* Turn it into an error for most cases, but allow some to override if
  necessary.
* Allow some cases to make it an error, while keeping it a warning by
  default.

Before we can decide which option to pick, we should get an idea of how
often this is being hit and which things it's being hit for.

Bug: T41936
Change-Id: I52926f410c30d1cd7e7fcd86465b16519fb5cbd2