ext{3,4}: Fix potential race when setversion ioctl updates inode

The EXT{3,4}_IOC_SETVERSION ioctl() updates i_ctime and i_generation
without i_mutex. This can lead to a race with the other operations that
update i_ctime. This is not a big issue but let's make the ioctl consistent
with how we handle e.g. other timestamp updates and use i_mutex to protect
inode changes.

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Signed-off-by: Jan Kara <jack@suse.cz>