udf: Apply uid/gid mount options also to new inodes & chown

Currently newly created files belong to current user despite
uid=<number> / gid=<number> mount options. This is confusing to users
(as owner of the file will change after remount / eviction from cache)
and also inconsistent with e.g. FAT with the same mount option. So apply
uid=<number> and gid=<number> also to newly created inodes and similarly
as FAT disallow to change owner of the file in this case.

Reported-by: Steve Kenton <skenton@ou.edu>
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>