IB/ehca: Forward event client-reregister-required to registered clients

This patch allows ehca to forward event client-reregister-required to
registered clients.  One such event is generated by a switch eg. after
its reboot.

Signed-off-by: Hoang-Nam Nguyen <hnguyen@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>