LU-12163 lnet: fix cpt locking

LU-12163 lnet: fix cpt locking

In lnet_select_pathway() the call to lnet_handle_send_case_locked()
can result in sd_cpt being changed. If this function returns
REPEAT_SEND, we'll go back to the again label. It is possible at
this time to initiate discovery, which will unlock the cpt.
If the local cpt isn't updated we could potentially be manipulating
the wrong cpt resulting in some form of corruption or dead lock.

Lustre-change: https://review.whamcloud.com/34607
Lustre-commit: f6d63067e1ec00009b9da5cdb263fe14e7e503e1

Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Change-Id: Ifd39b0d84f8cce859151f7cc900a082481dd7218
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Chris Horn <hornc@cray.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/36032
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>