Drivers: hv: vss: process deferred messages when we complete the transaction

Drivers: hv: vss: process deferred messages when we complete the transaction

In theory, the host is not supposed to issue any requests before be reply to
the previous one. In KVP we, however, support the following scenarios:
1) A message was received before userspace daemon registered;
2) A message was received while the previous one is still being processed.
In VSS we support only the former. Add support for the later, use
hv_poll_channel() to do the job.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Tested-by: Alex Ng <alexng@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Orabug: 25819105
(cherry picked from commit 38c06c29bada78c4805000bfb9b7f19cd691461b)
Signed-off-by: Jack Vogel <jack.vogel@oracle.com>