mlx4ib and mlx5ib: Set slid to zero in Ethernet completion struct

IB spec says that a lid should be ignored when link layer is Ethernet,
for example when building or parsing a CM request message (CA17-34).
However, since ib_lid_be16() and ib_lid_cpu16() validates the slid,
not only when link layer is IB, we set the slid to zero to prevent
false warnings in the kernel log.

Linux commit:
65389322b28f81cc137b60a41044c2d958a7b950

MFC after: 1 week
Reviewed by: kib
Sponsored by: Mellanox Technologies // NVIDIA Networking