ext3: preserve i_mode if ext2_set_acl() fails

ext3: preserve i_mode if ext2_set_acl() fails

Based on Ernesto A. Fernández's fix for ext2 (commit fe26569eb919), from
which the following description is taken:

> When changing a file's acl mask, ext2_set_acl() will first set the group
> bits of i_mode to the value of the mask, and only then set the actual
> extended attribute representing the new acl.
>
> If the second part fails (due to lack of space, for example) and the file
> had no acl attribute to begin with, the system will from now on assume
> that the mask permission bits are actual group permission bits, potentially
> granting access to the wrong users.
>
> Prevent this by only changing the inode mode after the acl has been set.

Cc: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>