IB/mlx4: Avoid field-overflowing memcpy()

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring array fields.

Use the ether_addr_copy() helper instead, as already done for smac.

Link: https://lore.kernel.org/r/20210616203744.1248551-1-keescook@chromium.org


Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>