IB/ehca: SRQ fixes to enable IPoIB CM

Fix ehca SRQ support so that IPoIB connected mode works:

 - Report max_srq > 0 if SRQ is supported
 - Report "last wqe reached" asynchronous event when base QP dies;
   this is required by the IB spec and IPoIB CM relies on receiving it
   when cleaning up.

Signed-off-by: Joachim Fenkes <fenkes@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>