IB/core: Use GRH when the path hop-limit > 0

According to IBTA spec v1.3 section 12.7.19, QPs should use GRH when
the path returned by the SA has hop-limit > 0. Currently, we do that
only for the > 1 case, fix that.

Fixes: 6d969a47 ('IB/sa: Add ib_init_ah_from_path()')
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>