Make code faster on platforms not supporting unaligned access by
default.
SPICE_UNALIGNED_CAST is just silencing possible alignment warning and,
if enabled, produces some logs, however in this case we know that the
pointer can be misaligned.
Use packed structures to tell compiler to generate best code possible.
For more details see comment on commit 74e50b57ae ("Make the
compiler work out better way to write unaligned memory").
Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Christophe Fergeau <cfergeau@redhat.com>