API1: ZSL buffers should be skipped for manual AF mode

ZSL counts on good auto focus (CAF). It is really tricky to enable ZSL for
manual focus mode. as it is bascically a locked focus mode, you can not tell
if the focus is good or not by reading the afstate.

Bug: 17577928
Change-Id: I68ff7d143e7d56f942bb00a8da6a9faea57b52a0