[ofw] [ofw'[Patch][umad] Avoid dangling reference

[Hefty, Sean]

> Some of the infiniband-diags can set the grh_present flag. I tested
> perfquery with GRHs quite some time ago and I think there are other
> diags which can do that too.

I didn't see where anything would set grh_present in my search of the source code.  There's a place in libibmad, but it's inside an if statement.  Maybe it gets set indirectly somehow?  Do you happen to know where it can be set?