LU-9716 osc: osc_extent_tree_dump0() implementation is suboptimal

LU-9716 osc: osc_extent_tree_dump0() implementation is suboptimal

Avoid looping in osc_extent_tree_dump() if debugging is disabled.
This helps us save some cpu ticks.

Change-Id: I492429d8a6de79f67b5923895ffa58b7fe3a100d
Seagate-bug-id: MRP-4469
Signed-off-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Reviewed-on: https://review.whamcloud.com/27866
Reviewed-by: Alexander Boyko <alexander.boyko@seagate.com>
Tested-by: Jenkins
Reviewed-by: Alexander Zarochentsev <alexander.zarochentsev@seagate.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>