b=23289 revert patch on 21828

b=23289 revert patch on 21828

this patch reverted change on bug 21828, because svc::srv_n_active_reqs
is dropped by ptlrpc_server_finish_request() now which is used to be
dropped by last calling of ptlrpc_server_drop_request, so recovery
thread has no refcount on svc::srv_n_active_reqs and we should just
remove these refcount changes.
This should also resovled issue of bug 21140, because logic in
ptlrpc_server_request_get() can be totally screwed up by
ptlrpc_server_active_request_inc/dec.