ctdbd: Set num_clients statistic from ctdb->num_clients
This fixes the problem of "ctdb statisticsreset" clearing the number of
clients even when there are active clients.
Values returned in statistics for frozen, recovering, memory_used are based on
the current state of CTDB and are not maintained as statistics. This should
include num_clients as well.
Currently ctdb->num_clients is unused. So use that to track the number of
clients and fill in statistics field only when requested.
Signed-off-by: Amitay Isaacs <amitay@gmail.com>
(cherry picked from commit
dc4ca816630ed44b419108da53421331243fb8c7)