Implemented `UnixBufferQueue::SetCapacity` so that `setsockopt` with `SO_RCVBUF` will not always return an error. Change-Id: I2d9be84633f84474fac64b379e9f89ef2751a094 Reviewed-on: https://review.haiku-os.org/c/haiku/+/6816 Reviewed-by: waddlesplash <[email protected]> Tested-by: Commit checker robot <[email protected]>