We are checking for gaps to previous bio_vec, which can
only detect back merges gaps. Moreover, at the point where
we check for a gap, we don't know if we will attempt a back
or a front merge. Thus, check for gap to prev in a back merge
attempt and check for a gap to next in a front merge attempt.
Signed-off-by: NJens Axboe <axboe@fb.com>
[sagig: Minor rename change]
Signed-off-by: NSagi Grimberg <sagig@mellanox.com>