RT_SIGFRAME_UC(sigframe).uc_sigmask.sig = args->blk_sigset;

blk_sigset is u64, but uc_sigmask.sig has type ulong [2], so
only a part of mask is restore here.

This patch reworks restoring of blocking masks symmetrically to dumping
these masks.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Tested-by: Alexander Kartashov <alekskartashov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>