ext4: allocate extended attribute value in vmalloc area

Now, extended attribute value maximum length is 64K. The memory
requested here does not need continuous physical addresses, so it is
appropriate to use kvmalloc to request memory. At the same time, it
can also cope with the situation that the extended attribute will
become longer in the future.

Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20221208023233.1231330-3-yebin@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org