[PATCH] rt2x00: Don't use changed_flags inside configure_packet_filter

We shouldn't use changed_flags when configuring the packet filter,
we work directly with the total_flags which is safe enough since
we already check if something has changed after we applied our
packet filtering flag rules.
Also make sure that when the packet filter is scheduled, the
rt2x00dev->interface.filter is cleared to make sure the drivers
will update the packet filter instead of failing at the check:
*total_flags == rt2x00dev->interface.filter

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>