[RESEND PATCH] binderfs: reserve devices for initial mount

[Christian Brauner]

On Fri, Jan 11, 2019 at 11:19:40AM +0100, Christian Brauner wrote:
> The binderfs instance in the initial ipc namespace will always have a
> reserve of 4 binder devices unless explicitly capped by specifying a lower
> value via the "max" mount option.
> This ensures when binder devices are removed (on accident or on purpose)
> they can always be recreated without risking that all minor numbers have
> already been used up.
> 
> Cc: Todd Kjos <tkjos at google.com>
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>

Cherry-picked this commit on top of char-misc-linus and it applied
cleanly. I hope I took the right branch?

Thanks!
Christian