linux: netfront contains two locking problems found by lockdep:

linux: netfront contains two locking problems found by lockdep:

1. rx_lock is a normal spinlock, and tx_lock is an irq spinlock.  This
   means that in normal use, tx_lock may be taken by an interrupt
   routine while rx_lock is held.  However, netif_disconnect_backend
   takes them in the order tx_lock->rx_lock, which could lead to a
   deadlock. Reverse them.
2. rx_lock can also be used in softirq context, so it should be
   taken/released with spin_(un)lock_bh.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>