LU-16062 ldlm: improve bl_timeout for prolong

LU-16062 ldlm: improve bl_timeout for prolong

If there is a client's RPC in hand, we can do a better job for
calculating the lock callback timeout as RPC has the info what
client thinks about this RPC timeout. Let's use it.

HPE-bug-id: LUS-8866, LUS-11074
Signed-off-by: Vitaly Fertman <c17818@cray.com>
Change-Id: Ibd67d37c1073d0d3cb2e08b532c801af0de116fe
Reviewed-on: https://es-gerrit.dev.cray.com/157782
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Tested-by: Jenkins Build User <nssreleng@cray.com>
Reviewed-on: https://review.whamcloud.com/48094
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Reviewed-by: Andriy Skulysh <andriy.skulysh@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>