IB/rdmavt: Add support for query_port, modify_port and get_port_immutable

rvt_query_port calls into the driver through a call back function
query_port_state to populate the rest of ib_port_attr elements.
rvt_modify_port calls into the driver if needed through a call back
function shut_down_port()

Signed-off-by: Harish Chegondi <harish.chegondi@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>