Hyper-V: storvsc: Enhance srb_status code handling.

Hyper-V: storvsc: Enhance srb_status code handling.

In hv_storvsc_io_request() when coring, prevent changing of the send channel
from the base channel to another one. storvsc_poll always probes on the base
channel.

Based upon conversations with Microsoft, changed the handling of srb_status
codes. Most we should never get, others yes. All are treated as retry-able
except for two. We should not get these statuses, but if we ever do, the I/O
state is not known.

Submitted by:	Alexander Sideropoulos <Alexander.Sideropoulos@netapp.com>
Reviewed by:	trasz, allanjude, whu
MFC after:	1 week
Sponsored by:	Netapp Inc
Differential Revision:	https://reviews.freebsd.org/D25756