LU-12462 osc: layout and chunkbits alignment mismatch

LU-12462 osc: layout and chunkbits alignment mismatch

In the discard case, the OSC fsync/writeback code asserts
that each OSC extent is fully covered by the fsync request.

It may happen that a start(or an end) of a component does not match
the first (the last) osc object extent start (end), which is aligned
by the cl_chunkbits which depends on the OST block size.

The requirement for the component alignment is LOV_MIN_STRIPE_SIZE
which is 64K, the ZFS block size could be in MBs.

Use an aligned by chunk size the fsync reqion in the assertion.

Fixes: 092ecd6612 ("LU-12462 osc: Do not assert for first extent")

Signed-off-by: Vitaly Fertman <c17818@cray.com>
Change-Id: I2ff47fc87c838239142ffc63bebafce3e9403f4e
Cray-bug-id: LUS-7498
Reviewed-on: https://review.whamcloud.com/35733
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>