netdevices.txt update

Just made a minor update to Documentation/networking/netdevices.txt, and 
thought I would take the opportunity to pass it around once again.
Even though this doc has existed for quite a while now, I still come 
across code that loves to violate these locking rules in various ways.
Comments and additions welcome

        Jeff


Network Devices, the Kernel, and You!


Introduction
============
The following is a random collection of documentation regarding
network devices.



struct net_device synchronization rules
=======================================
dev->open:
        Synchronization: rtnl_lock() semaphore.
        Context: process

dev->stop:
        Synchronization: rtnl_lock() semaphore.
        Context: process
        Note1: netif_running() is guaranteed false
        Note2: dev->poll() is guaranteed to be stopped

dev->do_ioctl:
        Synchronization: rtnl_lock() semaphore.
        Context: process

dev->get_stats:
        Synchronization: dev_base_lock rwlock.
        Context: nominally process, but don't sleep inside an rwlock

dev->hard_start_xmit:
        Synchronization: dev->xmit_lock spinlock.
        Context: BHs disabled
        Notes: netif_queue_stopped() is guaranteed false

dev->tx_timeout:
        Synchronization: dev->xmit_lock spinlock.
        Context: BHs disabled
        Notes: netif_queue_stopped() is guaranteed true

dev->set_multicast_list:
        Synchronization: dev->xmit_lock spinlock.
        Context: BHs disabled

dev->poll:
        Synchronization: __LINK_STATE_RX_SCHED bit in dev->state.  See
                dev_close code and comments in net/core/dev.c for more info.
        Context: softirq