acrn-manager message structure has a flexible member
payload[0], that risks to out-of-boundary memory access,
and usage of uninitialized variable.
And the req/ack message pairs has various types, which
extend mngr_msg. mngr_send_msg() requires programmer cast
the type of input messages to struct mngr_msg, that is
inconvenient.
We replace payload[0] with an union, which contains all
payload data. So that type cast for mngr_send_msg() is no
longer needed. And we can avoid potential out-of-boundary
memory accessing and using of uninitialized variable
Acked-by: Yan Like <like.yan@intel.com>
Signed-off-by: Tao Yuhong <yuhong.tao@intel.com>