vhost: prepare for slave requests
vhost: prepare for slave requests

send_vhost_message() is currently only used to send
replies, so it modifies message flags to perpare the
reply.

With upcoming channel for backend initiated request,
this function can be used to send requests.

This patch introduces a new send_vhost_reply() that
does the message flags modifications, and makes
send_vhost_message() generic.

Signed-off-by: Maxime Coquelin <9a2667dee3b90866bbc9c2696cff2b7d5616c95a@redhat.com>
Acked-by: Yuanhan Liu <5219796f50b7b6a5f4ac3e8f0a0f9501ee64a87c@fridaylinux.org>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk