[CASSINI]: Revert 'dont touch page_count'.

This reverts changeset fa4f0774
([CASSINI]: dont touch page_count) because it breaks the driver.

The local page counting added by this changeset did not account
for the asynchronous page count changes done by kfree_skb()
and friends.

The change adds extra atomics and on top of it all appears to be
totally unnecessary as well.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Nick Piggin <npiggin@suse.de>