libnetdriver: turn into network driver framework

The new implementation of this library provides abstractions for
network drivers, and should be used for all network drivers from now
on.  It provides the following functionality:

  - a function call table abstraction, hiding the details of the
    datalink protocol with simple parameters;
  - a state machine for sending and receiving packets, freeing the
    actual driver from keeping track of pending requests;
  - an abstraction for copying data from and to the network driver,
    freeing the actual driver from dealing with I/O vectors while at
    the same time providing a copy implementation which is more
    efficient than most current driver implementations;
  - a generalized implementation of zero-copy port-based I/O;
  - a clearer set of policies and defaults.

While the concept is very similar to lib{block,char,fs,input}driver,
one main difference is that libnetdriver now also takes care of SEF
initialization, mainly so that aspects such as recovery policies and
live-update aspects can be changed for all network drivers in a
single place.  As always, for the case that the provided message loop
is too restrictive, a set of more low-level message processing
functions is provided.

The netdriver API has been designed so as to allow alleviation of one
current protocol bottleneck: the fact that at most one send request
and one receive request may be pending at any time.  Changing this
aspect will however require a significant rewrite of libnetdriver,
and possibly debugging of drivers that are not able to cope with (in
particular) queuing multiple packets for transmission at once.

Beyond that, the design of the new API is based on the current
protocol, and may be changed/extended later to allow for non-ethernet
network drivers, exposure of link status, multicast address
configuration, suspend and resume, and any other features that are in
fact long overdue.

Change-Id: I47ec47e05852c42f92af04549d41524f928efec2
atl2: use new libnetdriver

Change-Id: I65de5d29a75d5f3101b2c5ab16a4b0d79bd77cc3
dec21140A: use new libnetdriver

Change-Id: I54be3b770e4d1fd320200c30e9e9073a7c1b405b
dp8390: use new libnetdriver

Change-Id: Ieaf6d605832d475f95fd9b06026b349dce7ee025