rt2x00: Remove obsolete rt2x00queue_align_payload

Since commit d1c3a37c ("mac80211:
clarify alignment docs, fix up alignment") removed the requirement
for a 4-byte aligned payload rt2x00queue_align_payload is obsolete
as mac80211 will align the payload when it passes the frame to the
net stack.

As a result we can remove the call to rt2x00queue_align_payload in the
rx path and since that's the last user we can remove
rt2x00queue_align_payload altogether.

One advantage is that we save some alignment operations for frames
that don't need to be aligned (for example beause they are not passed
to the net stack).

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