EX-7601 ofd: add checks to io_lnb_to_tx_lnb

EX-7601 ofd: add checks to io_lnb_to_tx_lnb

We should always be able to find the remote niobuf in the
local io range, if we can't, there's a bug.  So assert on
this.

We should also never have page level overlapping remote IOs,
at least until we have unaligned DIO.  (We can remove this
check when we combine the features.)

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I325d4a37d25c116e42621964e90b225b71fd8f1f
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53450
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>