RFC: adding queue number/size fields to ifnet

[Luigi Rizzo]

Hi,
it would be useful to have a common place with the indication of
NIC parameters such as number of tx/rx queues and their lengths.

Various 10G drivers do include this information in various places
in the softc, but there is no common place.
 
I was wondering if there is any objection to either or both 
of these options:

1. four fields to the struct ifnet (field names are bikeshed material
   and irrelevant for the discussion):
      if_tx_queues, if_rx_queues, if_tx_slots, if_rx_slots

2. a sysctl-like get/set method for key-value pairs (key is always a
   string, value is possibly one of a few simple types such as
   INT64, UINT64, STRING) so that we extend the system in the future,
   e.g. to handle RSS, flow control and whatnot.
      Of course this also requires to settle on names of features.

This is meant for low-frequency access to the parameters of the
device, so performance is not an issue. 

	cheers
	luigi