act: fix the logic of parsing actions

It is proved that actions are not always put from 0,
they could be discontinuous.

http://lists.infradead.org/pipermail/libnl/2014-April/001374.html

Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Thomas Haller <thaller@redhat.com>