Add new mlx5ib(4) driver to the kernel source tree which supports
Remote DMA over Converged Ethernet, RoCE, for the ConnectX-4 series of
PCI express network cards.

There is currently no user-space support and this driver only supports
kernel side non-routable RoCE V1. The krping kernel module can be used
to test this driver. Full user-space support including RoCE V2 will be
added as part of the ongoing upgrade to ibcore from Linux 4.9. Otherwise
this driver is feature equivalent to mlx4ib(4). The mlx5ib(4) kernel
module will only be built when WITH_OFED=YES is specified.

MFC after: 2 weeks
Sponsored by: Mellanox Technologies