1.Don't preallocate sigaction list since it's used only in the task context
2.Reduce the preserved item which is used only in the task context from 16 to 4
The total memory decrease from 1280B to 480B
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: Ib5d5a7365c7d443fc0e99c0d3ea943e85f67ca8c