IB/core: Set static rate in ib_init_ah_from_path()

The static rate from the path record should be put into the address
vector -- a long time ago the rate in the address attributes needed to
be a relative rate, which required more munging, but now that the
conversion from absolute to relative is done in the low-level driver,
it's easy for ib_init_ah_from_path() to put the absolute rate in.

Cc: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>