sys_rt_sigaction: fix sigset copying
sys_rt_sigaction: fix sigset copying

In practice, we always copy as many bytes as syscall param says
(8, or 16 on mips). However, malicious program can call sigaction
with wrong sigset size. Such syscall will result in EINVAL,
but we (strace) end up copying 128 bytes (sizeof(sigset_t)),
which copyes some garbage from stack after struct sigaction.

Now we always copy NSIG / 8 bytes (which is 8 bytes, or 16 on mips).

Signed-off-by: Denys Vlasenko <50fbbd36fe0f9c8261d4a3c762c8c29ffb35e48f@redhat.com>

geofft/strace,Infinitive-OS/platform_external_strace,xin3liang/platform_external_strace,bigzz/strace_android,Yu-AndroidM/android_external_strace,bnoordhuis/strace,android-ia/platform_external_strace,bigzz/strace_android,Saruta/strace,kapdop/android_external_strace,Distrotech/strace,DirtyUnicorns/android_external_strace,vrastogi/strace,CyanogenMod/android_external_strace,pombredanne/strace,DirtyUnicorns/android_external_strace,CyanogenMod/android_external_strace,Infinitive-OS/platform_external_strace,android-ia/platform_external_strace,MonkeyZZZZ/platform_external_strace,geekboxzone/lollipop_external_strace,Yu-AndroidM/android_external_strace,Distrotech/strace,Yu-AndroidM/android_external_strace,cuviper/strace,android-ia/platform_external_strace,Yu-AndroidM/android_external_strace,MonkeyZZZZ/platform_external_strace,vrastogi/strace,YUPlayGodDev/platform_external_strace,Distrotech/strace,bnoordhuis/strace,TeamExodus/external_strace,DirtyUnicorns/android_external_strace,TeamExodus/external_strace,Infinitive-OS/platform_external_strace,geofft/strace,kapdop/android_external_strace,lkundrak/strace,lkundrak/strace,vrastogi/strace,Distrotech/strace,vrastogi/strace,android-ia/platform_external_strace,CyanogenMod/android_external_strace,geekboxzone/mmallow_external_strace,YUPlayGodDev/platform_external_strace,vrastogi/strace,TeamExodus/external_strace,lkundrak/strace,AOSP-YU/platform_external_strace,cuviper/strace,cuviper/strace,pombredanne/strace,bigzz/strace_android,MonkeyZZZZ/platform_external_strace,MonkeyZZZZ/platform_external_strace,cuviper/strace,bnoordhuis/strace,geekboxzone/lollipop_external_strace,geekboxzone/lollipop_external_strace,Saruta/strace,pombredanne/strace,geofft/strace,kapdop/android_external_strace,kapdop/android_external_strace,DirtyUnicorns/android_external_strace,MonkeyZZZZ/platform_external_strace,TeamExodus/external_strace,Saruta/strace,xin3liang/platform_external_strace,YUPlayGodDev/platform_external_strace,android-ia/platform_external_strace,lkundrak/strace,bigzz/strace_android,CyanogenMod/android_external_strace,Yu-AndroidM/android_external_strace,bigzz/strace_android,AOSP-YU/platform_external_strace,AOSP-YU/platform_external_strace,AOSP-YU/platform_external_strace,geekboxzone/lollipop_external_strace,kapdop/android_external_strace,xin3liang/platform_external_strace,geekboxzone/mmallow_external_strace,geofft/strace,geekboxzone/lollipop_external_strace,Saruta/strace,Saruta/strace,geekboxzone/mmallow_external_strace,Infinitive-OS/platform_external_strace,cuviper/strace,Distrotech/strace,pombredanne/strace,DirtyUnicorns/android_external_strace,CyanogenMod/android_external_strace,YUPlayGodDev/platform_external_strace,xin3liang/platform_external_strace,YUPlayGodDev/platform_external_strace,TeamExodus/external_strace,geofft/strace,bnoordhuis/strace,geekboxzone/mmallow_external_strace,geekboxzone/mmallow_external_strace,Infinitive-OS/platform_external_strace,AOSP-YU/platform_external_strace