LU-18671 mdc: don't send empty rpc for DoM

LU-18671 mdc: don't send empty rpc for DoM

osc_page_gang_lookup() sends empty rpc to refresh a lock,
bases on cl_io lm_next_rpc_time from a thread storage.
mdc_lock_discard_pages() does not set time, and it is taken from a
osc_thread_info. Sometimes this leads to an empty rpc for a DoM,
outside of DoM component size.

LustreError: lustre-MDT0000-mdc-ffffa0816bceb000: operation ost_read
 to node 192.168.122.55@tcp failed: rc = -116

HPE-bug-id: LUS-12706
Fixes: 564070343ac4 ("LU-14711 osc: Notify server if cache discard takes a long time")
Signed-off-by: Alexander Boyko <alexander.boyko@hpe.com>
Change-Id: I36cdc2c697e2306e792241ecee77b442b24356ce
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57883
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andriy Skulysh <andriy.skulysh@hpe.com>
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>