LU-5548 ptlrpc: avoid list scan in ptlrpcd_check

LU-5548 ptlrpc: avoid list scan in ptlrpcd_check

ptlrpcd_check() always scan all requests on ptlrpc_request_set
and try to finish completed requests, this is low efficiency.
Even worse, l_wait_event() always checks condition for twice
before sleeping and one more time after waking up, which means
it will call ptlrpcd_check() for three times in each loop.

This patch will move completed requests at the head of list
in ptlrpc_check_set(), with this change ptlrpcd_check doesn't
need to scan all requests anymore.

Signed-off-by: Liang Zhen <liang.zhen@intel.com>
Signed-off-by: Mikhail Pershin <mike.pershin@intel.com>
Change-Id: I770016d4a2bcd51603b390b41427eb64ff52f71c
Reviewed-on: http://review.whamcloud.com/12265
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>