bdrv_mirror_top_pwritev() accesses the job object when active mirroring
is enabled. It disables this code during early initialisation while
s->job isn't set yet.
However, s->job is still set way too early when the job object isn't
fully initialised. For example, &s->ops_in_flight isn't initialised yet
and the in_flight bitmap doesn't exist yet. This causes crashes when a
write request comes in too early.
Move the assignment of s->job to when the mirror job is actually fully
initialised to make sure that the mirror_top driver doesn't access it
too early.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>