ipwireless: Remove endian-dependent bitfields

Remove endian-dependent bitfields and use bitmasks to transform
packet header bitfields from/to machine order.
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>