libertas: Fix alignment issues in libertas core

Data structures that come over the wire from the WLAN firmware must be packed.
This fixes alignment problems on the blackfin architecture and, reportedly, on
the AVR32.

This is a replacement for the previous version of this patch which had also
explicitly used get_unaligned_ macros.  As Johannes Berg pointed out, these
macros were unnecessary.

Signed-off-by: Andrey Yurovsky <andrey@cozybit.com>
Signed-off-by: Colin McCabe <colin@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>