This is an updated attempt to convert 9p to the new mount API. 9p is one of the last conversions needed, possibly because it is one of the trickier ones! I was able to test this to some degree, but I am not sure how to test all transports; there may well be bugs here. It would be great to get some feedback on whether this approach seems reasonable, and of course any further review or testing would be most welcome. V2: Address "make W=1" warnings from kernel test robot, comments from dhowells, and some kernel-doc comments for changed arguments. Thanks, -Eric
