core: limit number of states owned by client

a dirty work around NFS client/dCache misbehavior
add a client command to simulate open state id DoS

Acked-by: Paul Millar
(cherry picked from commit a51eb1ad3d0ddf49ba77b1c3fd2dac4066e1b0bf)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>