netxen: drop redudant spinlock

Some leftover code that makes use of adapter->lock in tx_timeout function,
which resets the interface under this lock. In close() when the workqueue
is flushed, prints the warning about sleeping with interrupts disabled
(when spinlock debug is enabled). The lock was required with private netxen
IOCTLs, which were removed a while ago.

Signed-off-by: Jeff Garzik <jeff@garzik.org>