lantiq: fix sleep with spinlock held in xrx200 network driver

lantiq: fix sleep with spinlock held in xrx200 network driver

In the xrx200_close() function we call napi_disable(), that could
sleep, with priv->hw->chan[i].lock held. This could lead to deadlock
and causes the kernel to complain.

Look at the code I couldn't convince myself about why we
need to protect that specific code part with the lock. IMHO there
seems no reason to protect the refcount variables, because AFAIK
ndo_close() and ndo_open() callbacks are already called with a
semaphore held. Neither I could figure out why napi_disable() have to
be called with that lock held. The only remaining code part for
which I could guess the lock is useful for is ltq_dma_close()
function call.

This patch reduces the lock to the said function call, avoiding the
sleep-with-spinlock-held situation

Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
[fold into 0025-NET-MIPS-lantiq-adds-xrx200-net.patch, backport to
kernel 4.4]
Signed-off-by: Mathias Kresin <dev@kresin.me>