IB/hfi1: Correctly report neighbor link down reason

The code to save the link down reason for reporting to the SMA
was in a location before the actual reason was read.  Move the
SMA link down reason assignment to a better location.

Reviewed-by: Easwar Hariharan <easwar.hariharan@intel.com>
Signed-off-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>