In preparation of replacing the statically allocated DMA buffers with
dynamically mapped skbs, centralize the allocation of RX skbs to rt2x00queue.c
and let rt2x00pci already use them.

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