[NetKVM] BZ#951070 - Fix debug printouts
[virtio-serial] bz#823818: add a missing feature bit.

Commit f5e27790 rewrote the add_buf usage using the indirect buffers
feature. Problem was that the guest didn't notify the device about
this change.
[virtio-serial] bz#823818: resend write request using a work item.

In commit f5e27790, the support for non-blocking write requests, causes
a bsod when the request resubmision was called from the dpc function.
The resubmision is now executed using a work item at a lower irql.
[virtio-serial] bz#823818: fix data corruption during writes.

Replace the indirect buffer usage added in commit f5e27790 to a
"handle one request at a time". Problem was that sometime the
indirect buffer was released before qemu tried to access it.
[virtio-serial] fix host notification when msi is disabled.

Related to commit 8fe2811b. If msi was not enabled (e.g. Windows
XP), an invalid interrupt object was used when sending notification
that the host is connected.