LU-6757 ldiskfs: acquire i_mutex lock for ext4_update_i_disksize

LU-6757 ldiskfs: acquire i_mutex lock for ext4_update_i_disksize

For RHEL 7.1 kernel version 3.10.0, i_mutex lock needs to be acquired
before calling ext4_update_i_disksize() to avoid races with truncate.

i_size_write() also needs locking around it (normally i_mutex), otherwise
on 32bit/SMP an update of i_size_seqcount can be lost, resulting in
subsequent i_size_read() calls spinning forever.

For large EA support, ext4_xattr_check_names() will return -EIO. This
patch fixes that by checking whether the large EA value is saved in an
external EA inode or not.

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: I095246cc1f7457defe87ca246edf98bbc051bc29
Reviewed-on: http://review.whamcloud.com/16012
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>