[ofw] winOFED 2.3 updates

[Hefty, Sean]

> If people want their SVN trunk commits since 2913 to be part of the 2.3
> release, you should let me know.

Please pull in commits 2928 and 2919.  These are both minor bug fixes - nothing critical.

2928:
winverbs/winmad: check return value of DeviceIoControl

We need to check the return value from DeviceIoControl before
calling GetOverlappedResult to avoid potential hangs.

2919:
libibumad: report port rate in Gbps

Port rate is currently reported as port speed, rather than in Gbps.