For x86 there are different SIGFRAME_OFFSET for native and compatible
tasks. In the next patches I will make SIGFRAME_OFFSET(rt_sigframe)
macro (depending on rt_sigframe).

As RESTORE_STACK_SIGFRAME used only for allocation sizes,
I don't want to introduce RESTORE_STACK_SIGFRAME(rt_sigframe)
dependency on rt_sigframe type. Let's just use for this porpose max
sigframe offset of native/compat tasks.

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>