The validation on the length of incoming packets performed in
storvsc_on_channel_callback() does not apply to unsolicited packets with ID
of 0 sent by Hyper-V.  Adjust the validation for such unsolicited packets.

Link: https://lore.kernel.org/r/20211007122828.469289-1-parri.andrea@gmail.com
Fixes: 91b1b640 ("scsi: storvsc: Validate length of incoming packet in storvsc_on_channel_callback()")
Reported-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>