9pfs: make multidevs=remap default

9pfs: make multidevs=remap default

1a6ed33cc5 introduced option multidevs=remap|forbid|warn and made
"warn" the default option.

As it turned out though, e.g. by several reports in conjunction with
following 9p client issue:

https://github.com/torvalds/linux/commit/850925a8133c73c4a2453c360b2c3beb3bab67c9

Many people are just ignoring this warning, or even do not notice the
warning at all. Therefore make multidevs=remap the new default option to
prevent people to run into such kind of severe misbehaviours in the first
place.

From performance PoV the runtime overhead of multidevs=remap is
neglectable with few or even just only one device being shared with the
same 9p export, expected to be constant Theta(1). The inode numbers
emitted to guest also just loose one bit (since 6b6aa8285d) for the 1st
device being shared.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <09cc84e5561f66b6a8cf49b3532c6c78a6acc806.1734876877.git.qemu_oss@crudebyte.com>