xfs: test case for handling io errors when reading extended attributes

xfs: test case for handling io errors when reading extended attributes

We've seen reports from the field panicking in xfs_trans_brelse after an
IO error when reading an attribute block.

sd 0:0:23:0: [sdx] tag#271 CDB: Read(16) 88 00 00 00 00 00 9b df 5e 78 00 00 00 08 00 00
critical medium error, dev sdx, sector 2615107192 op 0x0:(READ) flags 0x1000 phys_seg 1 prio class 2
XFS (sdx1): metadata I/O error in "xfs_da_read_buf+0xe1/0x140 [xfs]" at daddr 0x9bdf5678 len 8 error 61
BUG: kernel NULL pointer dereference, address: 00000000000000e0
...
RIP: 0010:xfs_trans_brelse+0xb/0xe0 [xfs]

Signed-off-by: Donald Douwsma <ddouwsma@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>