LU-14183 ldlm: wrong ldlm_add_waiting_lock usage

LU-14183 ldlm: wrong ldlm_add_waiting_lock usage

exp_bl_lock_at accounted the period since BLAST send until cancel RPC
came to server originally. LU-6032 started to update l_blast_sent for
expired locks which are still busy - prolonged locks when the timeout
expired. In fact, this is a good idea to cover not the whole period
but until any involved RPC comes - it avoids excessively large lock
callback timeouts - and the IO which does the lock prolong is also
able to re-start the AT cycle by updating the l_blast_sent.

Unfortunately, the change seems to be made occasionally as the main
prolong code was not adjusted accordingly.

Fixes: 292aa42e08 ("LU-6032 ldlm: don't disable softirq for exp_rpc_lock")
HPE-bug-id: LUS-9278
Signed-off-by: Vitaly Fertman <c17818@cray.com>
Change-Id: Idc598508fc13aa33ac9fce56f13310ca6fc819d4
Tested-by: Jenkins Build User <nssreleng@cray.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Alexander Boyko <c17825@cray.com>
Reviewed-on: https://review.whamcloud.com/40868
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: Andriy Skulysh <askulysh@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>