This macro allow to define magic constants without using weird
memory tweacks.
This remove some possible warning from some compiler and
make code more optimized as compiler is able to compute the
constant.
Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
spice-protocol comes with 2 headers to handle structure packing,
but controller_prot.h and foreign_menu_prot were both using their
own preprocessor definitions to handle packing. It's better to have
structure packing macros centralized since how it's done varies
between compilers, so it may need to change over time.
