IB/mlx4: Properly initialize GRH TClass and FlowLabel in AHs

commit 8c5122e4 upstream.

When this code was reworked for IBoE support the order of assignments
for the sl_tclass_flowlabel got flipped around resulting in
TClass & FlowLabel being permanently set to 0 in the packet headers.

This breaks IB routers that rely on these headers, but only affects
kernel users - libmlx4 does this properly for user space.

Cc: stable@vger.kernel.org
Fixes: fa417f7b ("IB/mlx4: Add support for IBoE")
Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>