[CORE] ib/mad: fix routing of vendor mads.

[CORE] ib/mad: fix routing of vendor mads.
SVN commit 2174 introduced an error that resulted in all
vendor MADs being routed to the local HCA driver.

This results in the ib-diag vendstat failing to receive
a response when trying to gather statistics about a remote
device.

We should only route vendor mads to the local HCA if the
mad is one of the mellanox vendor classes, the mad is not
a response, and the local HCA is the destination for the
mad.  Simplify both the send and receive processing to
be consistent in vendor mad handling.

Problem reported by Mohammad Sawalha.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
git-svn-id: svn://openib.tc.cornell.edu/gen1@2678 ad392aa1-c5ef-ae45-8dd8-e69d62a5ef86