IB/hfi1: Use bool in process_ecn

The process_ecn intends to return a bool value. However it is doing
so incorrectly by ANDing the fecn mask. The fecn bit is bit 31. Bool is
not a native data type and is up to the compiler to implement how it
sees fit. It is conceivable that this upper bit gets washed out.

Fix by converting to a bool properly.

Cc: stable@vger.kernel.org
Fixes: Commit fd2b562edca6 ("IB/hfi1: Pull FECN/BECN processing to a common place")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>