The existing method of telling if a channel is sub-channel in
vmbus_process_offer() is cumbersome. This new simple helper function
is preferred in future.
Signed-off-by: NDexuan Cui <decui@microsoft.com>
Reviewed-by: NMichael Kelley <mikelley@microsoft.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>